Salt, acid generator, resist composition and method for producing resist pattern

ABSTRACT

A salt capable of producing a resist pattern with excellent line edge roughness is represented by formula (I): 
     
       
         
         
             
             
         
       
     
     wherein, R 1  represents —(X 1 —O) o —R 5 , and o represents an integer of 0 to 6, R 5  represents a hydrocarbon group having 1 to 12 carbon atoms, X 1  represents a divalent hydrocarbon group having 2 to 12 carbon atoms, R 2  represents an alkyl group having 1 to 12 carbon atoms or the like, I represents an integer of 0 to 3, and when I is 2 or more, a plurality of R 2  may be the same or different from each other, R 3  and R 4  each represent a hydrogen atom or the like, m and n each represent 1 or 2, X 0  represents a single bond, —CH 2 —, —O— or —S—, and R 6  and R 7  each represent an alkyl group having 1 to 4 carbon atoms which has a fluorine atom or the like.

TECHNICAL FIELD

The present invention relates to a salt for acid generator which is usedfor fine processing of a semiconductor, an acid generator containing thesalt, a resist composition and a method for producing a resist pattern.

BACKGROUND ART

Patent Document 1 mentions a resist composition containing, as a saltfor an acid generator, a salt represented by the following formula:

Patent Document 2 mentions a salt represented by the following formula,and a resist composition containing the salt as an acid generator.

Patent Document 3 mentions a salt represented by the following formula,and a resist composition containing the salt as an acid generator.

Patent Document 4 mentions a salt represented by the following formula,and a resist composition containing the salt as an acid generator.

Patent Document 5 mentions a salt represented by the following formula,and a resist composition containing the salt as an acid generator.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP 2012-106980 A

Patent Document 2: JP 2015-143208 A

Patent Document 3: JP 2002-268223 A

Patent Document 4: JP 2012-168279 A

Patent Document 5: JP 2014-224095 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention provides a salt capable of producing a resistpattern with line edge roughness (LER) which is better than that of aresist pattern formed from the above-mentioned resist composition.

Means for Solving the Problems

The present invention includes the following inventions.

[1] A salt represented by formula (I):

wherein, in formula (I),

R¹ represents —(X¹—O)_(o)—R⁵, and o represents an integer of 0 to 6,

-   -   R⁵ represents a hydrocarbon group having 1 to 12 carbon atoms,

X¹ represents a divalent hydrocarbon group having 2 to 12 carbon atoms,

R² represents an alkyl group having 1 to 12 carbon atoms, and —CH₂—included in the alkyl group may be replaced by —O— or —CO—,

l represents an integer of 0 to 3, and when l is 2 or more, a pluralityof R² may be the same or different from each other,

R³ and R⁴ each independently represent a hydrogen atom, a hydroxy groupor a hydrocarbon group having 1 to 12 carbon atoms, and —CH₂— includedin the hydrocarbon group may be replaced by —O— or —CO—,

m and n each independently represent 1 or 2, when m is 2, two R³ are thesame or different from each other, and when n is 2, two R⁴ are the sameor different from each other,

X⁰ represents a single bond, —CH₂—, —O— or —S—, and

R⁶ and R⁷ each independently represent an alkyl group having 1 to 4carbon atoms which has a fluorine atom, or may be bonded to each otherto form a divalent hydrocarbon group having 2 to 8 carbon atoms whichhas a fluorine atom.

[2] The salt according to [1], wherein R³ and R⁴ are a hydrogen atom,and n and m are 2.[3] The salt according to [1] or [2], wherein o is 0, 1 or 2.[4] The salt according to any one of [1] to [3], wherein R⁶ and R⁷ eachindependently represent a trifluoromethyl group, a perfluoroethyl groupor may be bonded to each other to form a divalent hydrocarbon grouphaving 2 to 3 carbon atoms which has a fluorine atom.[5] An acid generator comprising the salt according to any one of [1] to[4].[6] A resist composition comprising the acid generator according to [5]and a resin having an acid-labile group.[7] The resist composition according to [6], wherein the resin having anacid-labile group includes at least two of a structural unit representedby formula (a1-1) and a structural unit represented by formula (a1-2):

wherein, in formula (a1-1) and formula (a1-2),

L^(a1) and L^(a2) each independently represent —O— or*—O—(CH₂)_(k1)—CO—O—, k1 represents an integer of 1 to 7, and *represents a bonding site to —CO—,

R^(a4) and R^(a5) each independently represent a hydrogen atom or amethyl group,

R^(a6) and R^(a7) each independently represent an alkyl group having 1to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms, or a group obtained by combining these groups,

m1 represents an integer of 0 to 14,

n1 represents an integer of 0 to 10, and

n1′ represents an integer of 0 to 3.

[8] The resist composition according to [6] or [7], further comprising asalt generating an acid having an acidity lower than that of an acidgenerated from the acid generator.[9] The resist composition according to any one of [6] to [8], furthercomprising a resin including a structural unit having a fluorine atom.[10] A method for producing a resist pattern, which comprises:(1) a step of applying the resist composition according to any one of[6] to [9] on a substrate,(2) a step of drying the applied composition to form a compositionlayer,(3) a step of exposing the composition layer,(4) a step of heating the exposed composition layer, and(5) a step of developing the heated composition layer.

Effects of the Invention

It is possible to produce a resist pattern with satisfactory line edgeroughness (LER) by using a resist composition using a salt of thepresent invention.

MODE FOR CARRYING OUT THE INVENTION

In the present specification, “(meth)acrylic monomer” means at least oneselected from the group consisting of a monomer having a structure of“CH₂═CH—CO—” and a monomer having a structure of “CH₂═C(CH₃)—CO—”.Similarly, “(meth)acrylate” and “(meth)acrylic acid” each mean “at leastone selected from the group consisting of acrylate and methacrylate” and“at least one selected from the group consisting of acrylic acid andmethacrylic acid”. When a structural unit having “CH₂═C(CH₃)—CO—” or“CH₂═CH—CO—” is exemplified, it is a structural unit having both groupsshall be similarly exemplified. In groups mentioned in the presentspecification, regarding groups capable of having both a linearstructure and a branched structure, they may have either the linear orbranched structure. When stereoisomers exist, all stereoisomers areincluded.

“group obtained by combining” means group obtained by combining two ormore of groups mentioned, and the valence of these groups may be changedappropriately depending on the binding mode.

In the present specification, “solid component of resist composition”means the total of components excluding the below-mentioned solvent (E)from the total amount of the resist composition.

<Salt Represented by Formula (I)>

The present invention relates to a salt represented by formula (I)(hereinafter sometimes referred to as “salt (I)”).

Of the salt (I), the side having negative charge is sometimes referredto as “anion (I)”, and the side having positive charge is sometimesreferred to as “cation (I)”.

Examples of the hydrocarbon group represented by R³, R⁴ and R⁵ includean aliphatic hydrocarbon group (a chain hydrocarbon group such as analkyl group, an alkenyl group and an alkynyl group, and an alicyclichydrocarbon group), an aromatic hydrocarbon group, and groups formed bycombining these groups.

Examples of the alkyl group include a methyl group, an ethyl group, ann-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group,a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptylgroup, a 2-ethylhexyl group, an n-octyl group, an n-nonyl group, ann-decyl group, an n-undecyl group, an n-dodecyl group and the like.

Examples of the alkenyl group include an ethenyl group, a propenylgroup, an isopropenyl group, a butenyl group, an isobutenyl group, atert-butenyl group, a pentenyl group, a hexenyl group, a heptenyl group,an octynyl group, an isooctynyl group, a nonenyl group and the like.

Examples of the alkynyl group include an ethynyl group, a propynylgroup, an isopropynyl group, a butynyl group, an isobutynyl group, atert-butynyl group, a pentynyl group, a hexynyl group, an octynyl group,a nonynyl group and the like.

The alicyclic hydrocarbon group may be either monocyclic or polycyclic,and examples of the monocyclic alicyclic hydrocarbon group includecycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, acyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctylgroup, a cycloheptyl group and a cyclodecyl group. Examples of thepolycyclic alicyclic hydrocarbon group include a decahydronaphthylgroup, an adamantyl group, a norbornyl group and an isobornyl group.

Examples of the aromatic hydrocarbon group include a phenyl group, anaphthyl group, an anthryl group and the like.

Examples of the group formed by combination include a group obtained bycombining an aromatic hydrocarbon group and an alkyl group (e.g., anaralkyl group, an alkylaryl group and the like) and a group obtained bycombining an alicyclic hydrocarbon group and an alkyl group (e.g., analicyclic hydrocarbon group-alkyl group-, an alkyl group-alicyclichydrocarbon group- and the like).

Examples of the aralkyl group include a benzyl group, a phenethyl groupand the like.

Examples of the alicyclic hydrocarbon group-alkyl group- includecycloalkylalkyl groups such as a cyclohexylmethyl group, acyclohexylethyl group and a 1-(adamantan-1-yl)alkan-1-yl group.

Examples of the alkyl group-alicyclic hydrocarbon group- includecycloalkyl groups having an alkyl group, such as a methylcyclohexylgroup, a dimethylcyclohexyl group and a 2-alkyladamantan-2-yl group.

Examples of the group in which —CH₂— included in a hydrocarbon group isreplaced by —O— or —CO— include a methoxy group, an ethoxy group, abutoxy group, a cyclohexyloxy group, a cyclohexylmethoxy group, anacetyl group, a methoxycarbonyl group, an acetyloxy group, abutoxycarbonyloxy group, a benzoyloxy group and the like.

Examples of the alkyl group represented by R² include a methyl group, anethyl group, an n-propyl group, an isopropyl group, an n-butyl group, asec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexylgroup, an n-heptyl group, a 2-ethylhexyl group, an n-octyl group, ann-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl groupand the like.

Examples of the divalent hydrocarbon group having 2 to 12 carbon atomsrepresented by X¹ include linear alkanediyl groups such as an ethylenegroup, a propane-1,3-diyl group, a butane-1,4-diyl group, apentane-1,5-diyl group, a hexane-1,6-diyl group, a heptane-1,7-diylgroup, an octane-1,8-diyl group, a nonane-1,9-diyl group, adecane-1,10-diyl group, a undecane-1,11-diyl group and adodecane-1,12-diyl group;

branched alkanediyl groups such as a propane-1,2-diyl group, a1-methylbutane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, apentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group;

cycloalkanediyl groups such as a cyclobutane-1,3-diyl group, acyclopentane-1,3-diyl group, a cyclohexane-1,4-diyl group and acyclooctane-1,5-diyl group; and

polycyclic divalent alicyclic hydrocarbon groups such as anorbornane-1,4-diyl group, a norbornane-2,5-diyl group, anadamantane-1,5-diyl group and an adamantane-2,6-diyl group.

The divalent hydrocarbon group having 2 to 12 carbon atoms representedby X¹ is preferably an alkanediyl group having 2 to 6 carbon atoms, morepreferably a linear alkanediyl group having 2 to 6 carbon atoms, andstill more preferably a linear alkanediyl group having 2 to 4 carbonatoms.

o is preferably an integer of 0 to 3, more preferably 0 or 1, and stillmore preferably 0.

l is preferably 0 or 1, and more preferably 0.

m is preferably 2.

n is preferably 2.

At least one of m and n is preferably 2, and more preferably, m and nare both 2.

R¹ is preferably a hydrocarbon group having 1 to 12 carbon atoms, analkoxyalkyl group having 2 to 18 carbon atoms or an alkoxyalkoxyalkylgroup having 3 to 24 carbon atoms, more preferably an alkyl group having1 to 6 carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms oran alkoxyalkoxyalkyl group having 3 to 16 carbon atoms, still morepreferably an alkyl group having 1 to 6 carbon atoms or an alkoxyalkylgroup having 2 to 12 carbon atoms, and yet more preferably an alkylgroup having 1 to 6 carbon atoms or an alkoxyalkyl group having 2 to 8carbon atoms.

R² is preferably a hydroxy group, an alkyl group having 1 to 6 carbonatoms, an alkoxy group having 1 to 6 carbon atoms, an alkylcarbonylgroup having 2 to 7 carbon atoms or an alkylcarbonyloxy group having 2to 7 carbon atoms, more preferably a hydroxy group, an alkyl grouphaving 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbonatoms, and still more preferably an alkoxy group having 1 to 4 carbonatoms.

R³ is preferably a hydrogen atom.

R⁴ is preferably a hydrogen atom.

Preferably, R³ and R⁴ are both hydrogen atoms.

X⁰ is preferably a single bond, —CH₂— or —O—, and more preferably —CH₂—or —O—.

Of these, the cation (I) is preferably a cation in which R³ and R⁴ are ahydrogen atom, and n and m are 2. The cation is more preferably a cationin which R³ and R⁴ are a hydrogen atom, n and m are 2, R¹ is an alkylgroup having 1 to 4 carbon atoms or an alkoxyalkyl group having 2 to 8carbon atoms, l is 0, and X⁰ is —CH₂— or —O—.

Examples of the cation (I) include the following cations and the like.

Examples of the alkyl group having 1 to 4 carbon atoms which has afluorine atom represented by R⁶ and R⁷ include fluorinated alkyl groupssuch as a difluoromethyl group, a trifluoromethyl group, a1,1-difluoroethyl group, a 2,2-difluoroethyl group, a2,2,2-trifluoroethyl group, a perfluoroethyl group, a1,1,2,2-tetrafluoropropyl group, a 1,1,2,2,3,3-hexafluoropropyl group, a2,2,3,3,3-pentafluoropropyl group, a1-(trifluoromethyl)-1,2,2,2-tetrafluoroethyl group, a perfluoropropylgroup, a 1,1,2,2-tetrafluorobutyl group, a 1,1,2,2,3,3-hexafluorobutylgroup, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a perfluorobutyl groupand a 1,1-bis(trifluoromethyl)-2,2,2-trifluoroethyl group. Of these, aperfluoroalkyl group is preferable, and a trifluoromethyl group and aperfluoroethyl group are more preferable.

Examples of the divalent hydrocarbon group having 2 to 8 carbon atomswhich has a fluorine atom formed by bonding R⁶ and R⁷ with each otherinclude perfluoroalkanediyl groups such as a perfluoroethylene group, aperfluoropropanediyl group, a perfluorobutanediyl group, aperfluoropentanediyl group and a perfluorohexanediyl group.

Examples of the anion (I) include the following an ions.

Specific examples of the salt (I) include salts obtained by optionallycombining the above-mentioned cation (I) and anion (I). Specificexamples of the salt (I) are shown in the following Tables.

In the following Tables, each symbol represents a symbol attached to astructure which represents the above-mentioned anion (I) and cation (I).For example, the salt (I-1) means a salt composed of an anionrepresented by formula (I-a-1) and a cation represented by formula(I-c-1) and is the following salt.

TABLE 1 Salt (I) Anion (I) Cation (I) (I-1) (I-a-1) (I-c-1) (I-2)(I-a-2) (I-c-1) (I-3) (I-a-3) (I-c-1) (I-4) (I-a-4) (I-c-1) (I-5)(I-a-5) (I-c-1) (I-6) (I-a-1) (I-c-2) (I-7) (I-a-2) (I-c-2) (I-8)(I-a-3) (I-c-2) (I-9) (I-a-4) (I-c-2) (I-10) (I-a-5) (I-c-2) (I-11)(I-a-1) (I-c-3) (I-12) (I-a-2) (I-c-3) (I-13) (I-a-3) (I-c-3) (I-14)(I-a-4) (I-c-3) (I-15) (I-a-5) (I-c-3) (I-16) (I-a-1) (I-c-4) (I-17)(I-a-2) (I-c-4) (I-18) (I-a-3) (I-c-4) (I-19) (I-a-4) (I-c-4) (I-20)(I-a-5) (I-c-4) (I-21) (I-a-1) (I-c-5) (I-22) (I-a-2) (I-c-5) (I-23)(I-a-3) (I-c-5) (I-24) (I-a-4) (I-c-5) (I-25) (I-a-5) (I-c-5) (I-26)(I-a-1) (I-c-6) (I-27) (I-a-2) (I-c-6) (I-28) (I-a-3) (I-c-6) (I-29)(I-a-4) (I-c-6) (I-30) (I-a-3) (I-c-6)

TABLE 2 Salt (I) Anion (I) Cation (I) (I-31) (I-a-1) (I-c-7) (I-32)(I-a-2) (I-c-7) (I-33) (I-a-3) (I-c-7) (I-34) (I-a-4) (I-c-7) (I-35)(I-a-5) (I-c-7) (I-36) (I-a-1) (I-c-8) (I-37) (I-a-2) (I-c-8) (I-38)(I-a-3) (I-c-8) (I-39) (I-a-4) (I-c-8) (I-40) (I-a-5) (I-c-8) (I-41)(I-a-1) (I-c-9) (I-42) (I-a-2) (I-c-9) (I-43) (I-a-3) (I-c-9) (I-44)(I-a-4) (I-c-9) (I-45) (I-a-5) (I-c-9) (I-46) (I-a-1) (I-c-10) (I-47)(I-a-2) (I-c-10) (I-48) (I-a-3) (I-c-10) (I-49) (I-a-4) (I-c-10) (I-50)(I-a-5) (I-c-10) (I-51) (I-a-1) (I-c-11) (I-52) (I-a-2) (I-c-11) (I-53)(I-a-3) (I-c-11) (I-54) (I-a-4) (I-c-11) (I-55) (I-a-5) (I-c-11) (I-56)(I-a-1) (I-c-12) (I-57) (I-a-2) (I-c-12) (I-58) (I-a-3) (I-c-12) (I-59)(I-a-4) (I-c-12) (I-60) (I-a-5) (I-c-12)

TABLE 3 Salt (I) Anion (I) Cation (I) (I-61) (I-a-1) (I-c-13) (I-62)(I-a-2) (I-c-13) (I-63) (I-a-3) (I-c-13) (I-64) (I-a-4) (I-c-13) (I-65)(I-a-5) (I-c-13) (I-66) (I-a-1) (I-c-14) (I-67) (I-a-2) (I-c-14) (I-68)(I-a-3) (I-c-14) (I-69) (I-a-4) (I-c-14) (I-70) (I-a-5) (I-c-14) (I-71)(I-a-1) (I-c-15) (I-72) (I-a-2) (I-c-15) (I-73) (I-a-3) (I-c-15) (I-74)(I-a-4) (I-c-15) (I-75) (I-a-5) (I-c-15) (I-76) (I-a-1) (I-c-16) (I-77)(I-a-2) (I-c-16) (I-78) (I-a-3) (I-c-16) (I-79) (I-a-4) (I-c-16) (I-80)(I-a-5) (I-c-16) (I-81) (I-a-1) (I-c-17) (I-82) (I-a-2) (I-c-17) (I-83)(I-a-3) (I-c-17) (I-84) (I-a-4) (I-c-17) (I-85) (I-a-5) (I-c-17) (I-86)(I-a-1) (I-c-18) (I-87) (I-a-2) (I-c-18) (I-88) (I-a-3) (I-c-18) (I-89)(I-a-4) (I-c-18) (I-90) (I-a-5) (I-c-18)

TABLE 4 Salt (I) Anion (I) Cation (I) (I-91) (I-a-1) (I-c-19) (I-92)(I-a-2) (I-c-19) (I-93) (I-a-3) (I-c-19) (I-94) (I-a-4) (I-c-19) (I-95)(I-a-5) (I-c-19) (I-96) (I-a-1) (I-c-20) (I-97) (I-a-2) (I-c-20) (I-98)(I-a-3) (I-c-20) (I-99) (I-a-4) (I-c-20) (I-100) (I-a-5) (I-c-20)(I-101) (I-a-1) (I-c-21) (I-102) (I-a-2) (I-c-21) (I-103) (I-a-3)(I-c-21) (I-104) (I-a-4) (I-c-21) (I-105) (I-a-5) (I-c-21) (I-106)(I-a-1) (I-c-22) (I-107) (I-a-2) (I-c-22) (I-108) (I-a-3) (I-c-22)(I-109) (I-a-4) (I-c-22) (I-110) (I-a-5) (I-c-22) (I-111) (I-a-1)(I-c-23) (I-112) (I-a-2) (I-c-23) (I-113) (I-a-3) (I-c-23) (I-114)(I-a-4) (I-c-23) (I-115) (I-a-5) (I-c-23) (I-116) (I-a-1) (I-c-24)(I-117) (I-a-2) (I-c-24) (I-118) (I-a-3) (I-c-24) (I-119) (I-a-4)(I-c-24) (I-120) (I-a-3) (I-c-24)

TABLE 5 Salt (I) Anion (I) Cation (I) (I-121) (I-a-1) (I-c-25) (I-122)(I-a-2) (I-c-25) (I-123) (I-a-3) (I-c-25) (I-124) (I-a-4) (I-c-25)(I-125) (I-a-5) (I-c-25) (I-126) (I-a-1) (I-c-26) (I-127) (I-a-2)(I-c-26) (I-128) (I-a-3) (I-c-26) (I-129) (I-a-4) (I-c-26) (I-130)(I-a-5) (I-c-26) (I-131) (I-a-1) (I-c-27) (I-132) (I-a-2) (I-c-27)(I-133) (I-a-3) (I-c-27) (I-134) (I-a-4) (I-c-27) (I-135) (I-a-5)(I-c-27) (I-136) (I-a-1) (I-c-28) (I-137) (I-a-2) (I-c-28) (I-138)(I-a-3) (I-c-28) (I-139) (I-a-4) (I-c-28) (I-140) (I-a-5) (I-c-28)(I-141) (I-a-1) (I-c-29) (I-142) (I-a-2) (I-c-29) (I-143) (I-a-3)(I-c-29) (I-144) (I-a-4) (I-c-29) (I-145) (I-a-5) (I-c-29) (I-146)(I-a-1) (I-c-30) (I-147) (I-a-2) (I-c-30) (I-148) (I-a-3) (I-c-30)(I-149) (I-a-4) (I-c-30) (I-150) (I-a-5) (I-c-30)

TABLE 6 Salt (I) Anion (I) Cation (I) (I-151) (I-a-1) (I-c-31) (I-152)(I-a-2) (I-c-31) (I-153) (I-a-3) (I-c-31) (I-154) (I-a-4) (I-c-31)(I-155) (I-a-5) (I-c-31) (I-156) (I-a-1) (I-c-32) (I-157) (I-a-2)(I-c-32) (I-158) (I-a-3) (I-c-32) (I-159) (I-a-4) (I-c-32) (I-160)(I-a-5) (I-c-32) (I-161) (I-a-1) (I-c-33) (I-162) (I-a-2) (I-c-33)(I-163) (I-a-3) (I-c-33) (I-164) (I-a-4) (I-c-33) (I-165) (I-a-5)(I-c-33) (I-166) (I-a-1) (I-c-34) (I-167) (I-a-2) (I-c-34) (I-168)(I-a-3) (I-c-34) (I-169) (I-a-4) (I-c-34) (I-170) (I-a-5) (I-c-34)(I-171) (I-a-1) (I-c-35) (I-172) (I-a-2) (I-c-35) (I-173) (I-a-3)(I-c-35) (I-174) (I-a-4) (I-c-35) (I-175) (I-a-5) (I-c-35) (I-176)(I-a-1) (I-c-36) (I-177) (I-a-2) (I-c-36) (I-178) (I-a-3) (I-c-36)(I-179) (I-a-4) (I-c-36) (I-180) (I-a-5) (I-c-36) (I-181) (I-a-1)(I-c-37) (I-182) (I-a-2) (I-c-37) (I-183) (I-a-3) (I-c-37) (I-184)(I-a-4) (I-c-37) (I-185) (I-a-5) (I-c-37) (I-186) (I-a-1) (I-c-38)(I-187) (I-a-2) (I-c-38) (I-188) (I-a-3) (I-c-38) (I-189) (I-a-4)(I-c-38) (I-190) (I-a-5) (I-c-38) (I-191) (I-a-1) (I-c-39) (I-192)(I-a-2) (I-c-39) (I-193) (I-a-3) (I-c-39) (I-194) (I-a-4) (I-c-39)(I-195) (I-a-5) (I-c-39) (I-196) (I-a-1) (I-c-40) (I-197) (I-a-2)(I-c-40) (I-198) (I-a-3) (I-c-40) (I-199) (I-a-4) (I-c-40) (I-200)(I-a-5) (I-c-40) (I-201) (I-a-1) (I-c-41) (I-202) (I-a-2) (I-c-41)(I-203) (I-a-3) (I-c-41) (I-204) (I-a-4) (I-c-41) (I-205) (I-a-5)(I-c-41) (I-206) (I-a-1) (I-c-42) (I-207) (I-a-2) (I-c-42) (I-208)(I-a-3) (I-c-42) (I-209) (I-a-4) (I-c-42) (I-210) (I-a-5) (I-c-42)(I-211) (I-a-1) (I-c-43) (I-212) (I-a-2) (I-c-43) (I-213) (I-a-3)(I-c-43) (I-214) (I-a-4) (I-c-43) (I-215) (I-a-5) (I-c-43) (I-216)(I-a-1) (I-c-44) (I-217) (I-a-2) (I-c-44) (I-218) (I-a-3) (I-c-44)(I-219) (I-a-4) (I-c-44) (I-220) (I-a-5) (I-c-44) (I-221) (I-a-1)(I-c-45) (I-222) (I-a-2) (I-c-45) (I-223) (I-a-3) (I-c-45) (I-224)(I-a-4) (I-c-45) (I-225) (I-a-5) (I-c-45) (I-226) (I-a-1) (I-c-46)(I-227) (I-a-2) (I-c-46) (I-228) (I-a-3) (I-c-46) (I-229) (I-a-4)(I-c-46) (I-230) (I-a-5) (I-c-46)

Of these salts, the salt (I) preferably includes salt (I-1), salt (I-2),salt (I-5), salt (I-6), salt (I-7), salt (I-10), salt (I-11), salt(I-12), salt (I-15), salt (I-16), salt (I-17), salt (I-20), salt (I-41),salt (I-42), salt (I-45), salt (I-61), salt (I-62), salt (I-65), salt(I-66), salt (I-67), salt (I-70), salt (I-71), salt (I-72), salt (I-75),salt (I-76), salt (I-77) and salt (I-80).

<Method for Producing Salt (I)>

The salt (I) can be produced by reacting a salt represented by formula(I-a) with a salt represented by formula (I-b) in a solvent:

wherein all symbols are the same as defined above.

Examples of the solvent in this reaction include chloroform,acetonitrile, ion-exchanged water and the like.

The reaction temperature is usually 0° C. to 80° C., and the reactiontime is usually 0.5 hours to 24 hours.

The salt represented by formula (I-b) includes salts represented by thefollowing formulas, which are easily available on the market.

The salt represented by formula (I-a) can be produced, for example, byreacting a compound represented by formula (I-c) with a compoundrepresented by formula (I-d) in the presence of phosphorus pentoxide andmethanesulfonic acid:

wherein all symbols are the same as defined above.

The reaction temperature is usually 0° C. to 80° C., and the reactiontime is usually 0.5 hour to 24 hours.

The compound represented by formula (I-d) includes compounds representedby the following formulas, which are easily available on the market.

The compound represented by formula (I-c) can be produced, for example,by reacting a compound represented by formula (I-e) with a compoundrepresented by formula (I-f) in the presence of a base in a solvent:

wherein all symbols are the same as defined above.

Examples of the base in this reaction include potassium carbonate,potassium iodide and the like.

Examples of the solvent in this reaction include chloroform,acetonitrile, acetone, tetrahydrofuran and the like.

The reaction temperature is usually 0° C. to 80° C., and the reactiontime is usually 0.5 hour to 36 hours.

The compound represented by formula (I-e) includes compounds representedby the following formulas, which are easily available on the market.

The compound represented by formula (I-f) includes compounds representedby the following formulas, which are easily available on the market.

<Acid Generator>

The acid generator of the present invention is an acid generatorincluding the salt (I). The acid generator may include one salt (I) ormay include two or more salts (I).

The acid generator of the present invention may include, in addition tothe salt (I), an acid generator known in the resist field (hereinaftersometimes referred to as “acid generator (B)”). The acid generator (B)may be used alone, or two or more acid generators may be used incombination.

Either nonionic or ionic acid generator may be used as the acidgenerator (B). Examples of the nonionic acid generator include sulfonateesters (e.g., 2-nitrobenzyl ester, aromatic sulfonate, oxime sulfonate,N-sulfonyloxyimide, sulfonyloxyketone, diazonaphthoquinone 4-sulfonate),sulfones (e.g., disulfone, ketosulfone, sulfonyldiazomethane) and thelike. Typical examples of the ionic acid generator include onium saltscontaining an onium cation (e.g., diazonium salt, phosphonium salt,sulfonium salt, iodonium salt). Examples of the anion of the onium saltinclude sulfonic acid anion, sulfonylimide anion, sulfonylmethide anionand the like.

Specific examples of the acid generator (B) include compounds generatingan acid upon exposure to radiation mentioned in JP 63-26653 A, JP55-164824 A, JP 62-69263 A, JP 63-146038 A, JP 63-163452 A, JP 62-153853A, JP 63-146029 A, U.S. Pat. Nos. 3,779,778, 3,849,137, DE Patent No.3914407 and EP Patent No. 126,712. Compounds produced by a known methodmay also be used. Two or more acid generators (B) may also be used incombination.

The acid generator (B) is preferably a fluorine-containing acidgenerator, and more preferably a salt represented by formula (B1)(hereinafter sometimes referred to as “acid generator (B1)”, excludingthe salt (I)):

wherein, in formula (B1),

Q^(b1) and Q^(b2) each independently represent a fluorine atom or aperfluoroalkyl group having 1 to 6 carbon atoms,

L^(b1) represents a divalent saturated hydrocarbon group having 1 to 24carbon atoms, —CH₂— included in the divalent saturated hydrocarbon groupmay be replaced by —O— or —CO—, and a hydrogen atom included in thedivalent saturated hydrocarbon group may be substituted with a fluorineatom or a hydroxy group,

Y represents a methyl group which may have a substituent or an alicyclichydrocarbon group having 3 to 18 carbon atoms which may have asubstituent, and —CH₂— included in the alicyclic hydrocarbon group maybe replaced by —O—, —S(O)₂— or —CO—, and

Z1⁺ represents an organic cation.

Examples of the perfluoroalkyl group represented by Q^(b1) and Q^(b2)include a trifluoromethyl group, a perfluoroethyl group, aperfluoropropyl group, a perfluoroisopropyl group, a perfluorobutylgroup, a perfluorosec-butyl group, a perfluorotert-butyl group, aperfluoropentyl group and a perfluorohexyl group.

Preferably, Q^(b1) and Q^(b2) are each independently a fluorine atom ora trifluoromethyl group, and more preferably, both are fluorine atoms.

Examples of the divalent saturated hydrocarbon group in L^(b1) include alinear alkanediyl group, a branched alkanediyl group, and a monocyclicor polycyclic divalent alicyclic saturated hydrocarbon group, or thedivalent saturated hydrocarbon group may be a group formed by combiningtwo or more of these groups.

Specific examples thereof include linear alkanediyl groups such as amethylene group, an ethylene group, a propane-1,3-diyl group, abutane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diylgroup, a heptane-1,7-diyl group, an octane-1,8-diyl group, anonane-1,9-diyl group, a decane-1,10-diyl group, an undecane-1,11-diylgroup, a dodecane-1,12-diyl group, a tridecane-1,13-diyl group, atetradecane-1,14-diyl group, a pentadecane-1,15-diyl group, ahexadecane-1,16-diyl group and a heptadecane-1,17-diyl group;

branched alkanediyl groups such as an ethane-1,1-diyl group, apropane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diylgroup, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a2-methylbutane-1,4-diyl group;

monocyclic divalent alicyclic saturated hydrocarbon groups which arecycloalkanediyl groups such as a cyclobutane-1,3-diyl group, acyclopentane-1,3-diyl group, a cyclohexane-1,4-diyl group and acyclooctane-1,5-diyl group; and

polycyclic divalent alicyclic saturated hydrocarbon groups such as anorbornane-1,4-diyl group, a norbornane-2,5-diyl group, anadamantane-1,5-diyl group and an adamantane-2,6-diyl group.

The group in which —CH₂— included in the divalent saturated hydrocarbongroup represented by L^(b1) is replaced by —O— or —CO— includes, forexample, a group represented by any one of formula (b1-1) to formula(b1-3). In groups represented by formula (b1-1) to formula (b1-3) andgroups represented by formula (b1-4) to formula (b1-1) which arespecific examples thereof, * and ** represent a bonding site, and *represents a bonding site to —Y.

In formula (b1-1),

L^(b2) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 22 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom,

L^(b3) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 22 carbon atoms, a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom or ahydroxy group, and —CH₂— included in the saturated hydrocarbon group maybe replaced by —O— or —CO—, and

the total number of carbon atoms of L^(b2) and L^(b3) is 22 or less.

In formula (b1-2),

L^(b4) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 22 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom,

L^(b5) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 22 carbon atoms, a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom or ahydroxy group, and —CH₂— included in the saturated hydrocarbon group maybe replaced by —O— or —CO—, and

the total number of carbon atoms of L^(b4) and L^(b)S is 22 or less.

In formula (b1-3),

L^(b6) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 23 carbon atoms, a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom or ahydroxy group,

L^(b7) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 23 carbon atoms, a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom or ahydroxy group, and —CH₂— included in the saturated hydrocarbon group maybe replaced by —O— or —CO—, and

the total number of carbon atoms of L^(b6) and L^(b7) is 23 or less.

In groups represented by formula (b1-1) to formula (b1-3), when —CH₂—included in the saturated hydrocarbon group is replaced by —O— or —CO—,the number of carbon atoms before replacement is taken as the number ofcarbon atoms of the saturated hydrocarbon group.

Examples of the divalent saturated hydrocarbon group include those whichare the same as the divalent saturated hydrocarbon group of L^(b1).

L^(b2) is preferably a single bond.

L^(b3) is preferably a divalent saturated hydrocarbon group having 1 to4 carbon atoms.

L^(b4) is preferably a divalent saturated hydrocarbon group having 1 to8 carbon atoms, and a hydrogen atom included in the divalent saturatedhydrocarbon group may be substituted with a fluorine atom.

L^(b5) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 8 carbon atoms.

L^(b6) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 4 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom.

L^(b7) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 18 carbon atoms, a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom or ahydroxy group, and —CH₂— included in the divalent saturated hydrocarbongroup may be replaced by —O— or —CO—.

The group in which —CH₂— included in the divalent saturated hydrocarbongroup represented by L^(b1) is replaced by —O— or —CO— is preferably agroup represented by formula (b1-1) or formula (b1-3).

Examples of the group represented by formula (b1-1) include groupsrepresented by formula (b1-4) to formula (b1-8).

In formula (b1-4),

L^(b8) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 22 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom or ahydroxy group.

In formula (b1-5),

L^(b9) represents a divalent saturated hydrocarbon group having 1 to 20carbon atoms, and —CH₂— included in the divalent saturated hydrocarbongroup may be replaced by —O— or —CO—.

L^(b10) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 19 carbon atoms, and a hydrogen atom included in thedivalent saturated hydrocarbon group may be substituted with a fluorineatom or a hydroxy group, and

the total number of carbon atoms of L^(b9) and L^(b10) is 20 or less.

In formula (b1-6),

L^(b11) represents a divalent saturated hydrocarbon group having 1 to 21carbon atoms,

L^(b12) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 20 carbon atoms, and a hydrogen atom included in thedivalent saturated hydrocarbon group may be substituted with a fluorineatom or a hydroxy group, and

the total number of carbon atoms of L^(b11) and L^(b12) is 21 or less.

In formula (b1-7),

L^(b13) represents a divalent saturated hydrocarbon group having 1 to 19carbon atoms,

L^(b14) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 18 carbon atoms, and —CH₂-included in the divalentsaturated hydrocarbon group may be replaced by —O— or —CO—,

L^(b15) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 18 carbon atoms, and a hydrogen atom included in thedivalent saturated hydrocarbon group may be substituted with a fluorineatom or a hydroxy group, and

the total number of carbon atoms of L^(b13) to L^(b15) is 19 or less.

In formula (b1-8),

L^(b16) represents a divalent saturated hydrocarbon group having 1 to 18carbon atoms, and —CH₂— included in the divalent saturated hydrocarbongroup may be replaced by —O— or —CO—,

L^(b17) represents a divalent saturated hydrocarbon group having 1 to 18carbon atoms,

L^(b18) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 17 carbon atoms, and a hydrogen atom included in thedivalent saturated hydrocarbon group may be substituted with a fluorineatom or a hydroxy group, and

the total number of carbon atoms of L^(b16) to L^(b18) is 19 or less.

L^(b8) is preferably a divalent saturated hydrocarbon group having 1 to4 carbon atoms.

L^(b9) is preferably a divalent saturated hydrocarbon group having 1 to8 carbon atoms.

L^(b10) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 19 carbon atoms, and more preferably a single bond ora divalent saturated hydrocarbon group having 1 to 8 carbon atoms.

L^(b11) is preferably a divalent saturated hydrocarbon group having 1 to8 carbon atoms.

L^(b12) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 8 carbon atoms.

L^(b13) is preferably a divalent saturated hydrocarbon group having 1 to12 carbon atoms.

L^(b14) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 6 carbon atoms.

L^(b15) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 18 carbon atoms, and more preferably a single bond ora divalent saturated hydrocarbon group having 1 to 8 carbon atoms.

L^(b16) is preferably a divalent saturated hydrocarbon group having 1 to12 carbon atoms.

L^(b17) is preferably a divalent saturated hydrocarbon group having 1 to6 carbon atoms.

L^(b18) is preferably a single bond or a divalent saturated hydrocarbongroup having 1 to 17 carbon atoms, and more preferably a single bond ora divalent saturated hydrocarbon group having 1 to 4 carbon atoms.

Examples of the group represented by formula (b1-3) include groupsrepresented by formula (b1-9) to formula (b1-11).

In formula (b1-9),

L^(b19) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 23 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom,

L^(b20) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 23 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom, ahydroxy group or an alkylcarbonyloxy group, —CH₂— included in thealkylcarbonyloxy group may be replaced by —O— or —CO—, and a hydrogenatom included in the alkylcarbonyloxy group may be substituted with ahydroxy group, and

the total number of carbon atoms of L^(b19) and L^(b20) is 23 or less.

In formula (b1-10),

L^(b21) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 21 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom,

L^(b22) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 21 carbon atoms,

L^(b23) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 21 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom, ahydroxy group or an alkylcarbonyloxy group, —CH₂— included in thealkylcarbonyloxy group may be replaced by —O— or —CO—, and a hydrogenatom included in the alkylcarbonyloxy group may be substituted with ahydroxy group, and

the total number of carbon atoms of L^(b21), L^(b22) and L^(b23) is 21or less.

In formula (b1-1),

L^(b24) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 20 carbon atoms, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom,

L^(b25) represents a divalent saturated hydrocarbon group having 1 to 21carbon atoms,

L^(b26) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 20 carbon atoms, a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a fluorine atom, ahydroxy group or an alkylcarbonyloxy group, —CH₂— included in thealkylcarbonyloxy group may be replaced by —O— or —CO—, and a hydrogenatom included in the alkylcarbonyloxy group may be substituted with ahydroxy group, and

the total number of carbon atoms of L^(b24), L^(b25) and L^(b26) is 21or less.

In groups represented by formula (b1-9) to formula (b1-11), when ahydrogen atom included in the saturated hydrocarbon group is substitutedwith an alkylcarbonyloxy group, the number of carbon atoms beforesubstitution is taken as the number of carbon atoms of the saturatedhydrocarbon group.

Examples of the alkylcarbonyloxy group include an acetyloxy group, apropionyloxy group, a butyryloxy group, a cyclohexylcarbonyloxy group,an adamantylcarbonyloxy group and the like.

Examples of the group represented by formula (b1-4) include thefollowings.

Examples of the group represented by formula (b1-5) include thefollowings:

Examples of the group represented by formula (b1-6) include thefollowings.

Examples of the group represented by formula (b1-7) include thefollowings.

Examples of the group represented by formula (b1-8) include thefollowings.

Examples of the group represented by formula (b1-2) include thefollowings.

Examples of the group represented by formula (b1-9) include thefollowings.

Examples of the group represented by formula (b1-10) include thefollowings.

Examples of the group represented by formula (b1-1) include thefollowings.

Examples of the alicyclic hydrocarbon group represented by Y includegroups represented by formula (Y1) to formula (Y11) and formula (Y36) toformula (Y38).

When —CH₂— included in the alicyclic hydrocarbon group represented by Yis replaced by —O—, —S(O)₂— or —CO—, the number may be 1, or 2 or more.Examples of such group include groups represented by formula (Y12) toformula (Y35) and formula (Y39) to formula (Y41).

The alicyclic hydrocarbon group represented by Y is preferably a grouprepresented by any one of formula (Y1) to formula (Y20), formula (Y26),formula (Y27), formula (Y30), formula (Y31), formula (Y39) and formula(Y40), more preferably a group represented by formula (Y11), formula(Y15), formula (Y16), formula (Y20), formula (Y26), formula (Y27),formula (Y30), formula (Y31), formula (Y39) or formula (Y40), and stillmore preferably a group represented by formula (Y11), formula (Y15),formula (Y20), formula (Y30), formula (Y39) or formula (Y40).

When the alicyclic hydrocarbon group represented by Y is a spiro ringincluding an oxygen atom such as formula (Y28) to formula (Y35) orformula (Y39) to formula (Y40), the alkanediyl group between two oxygenatoms preferably has one or more fluorine atoms. Of alkanediyl groupsincluded in a ketal structure, it is preferable that a methylene groupadjacent to the oxygen atom is not substituted with a fluorine atom.

Examples of the substituent of the methyl group represented by Y includea halogen atom, a hydroxy group, an alicyclic hydrocarbon group having 3to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbonatoms, a glycidyloxy group, a —(CH₂)_(ja)—CO—O—R^(b1) group or a—(CH₂)_(ja)—O—CO—R^(b1) group (wherein R^(b1) represents an alkyl grouphaving 1 to 16 carbon atoms, an alicyclic hydrocarbon group having 3 to16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbonatoms, or groups obtained by combining these groups, ja represents aninteger of 0 to 4, and —CH₂— included in an alkyl group having 1 to 16carbon atoms and an alicyclic hydrocarbon group having 3 to 16 carbonatoms may be replaced by —O—, —S(O)₂— or —CO—) and the like.

Examples of the substituent of the alicyclic hydrocarbon grouprepresented by Y include a halogen atom, a hydroxy group, an alkyl grouphaving 1 to 12 carbon atoms which may be substituted with a hydroxygroup, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, analkoxy group having 1 to 12 carbon atoms, an aromatic hydrocarbon grouphaving 6 to 18 carbon atoms, an aralkyl group having 7 to 21 carbonatoms, an alkylcarbonyl group having 2 to 4 carbon atoms, a glycidyloxygroup, a —(CH₂)_(ja)—CO—O—R^(b1) group or —(CH₂)_(ja)—O—CO—R^(b1) group(wherein R^(b1) represents an alkyl group having 1 to 16 carbon atoms,an alicyclic hydrocarbon group having 3 to 16 carbon atoms or anaromatic hydrocarbon group having 6 to 18 carbon atoms, or groupsobtained by combining these groups, ja represents an integer of 0 to 4,and —CH₂— included in the alkyl group having 1 to 16 carbon atoms andthe alicyclic hydrocarbon group having 3 to 16 carbon atoms may bereplaced by —O—, —S(O)₂— or —CO—).

Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom.

The alicyclic hydrocarbon group includes, for example, a cyclopentylgroup, a cyclohexyl group, a methylcyclohexyl group, adimethylcyclohexyl group, a cycloheptyl group, a cyclooctyl group, anorbornyl group, an adamantyl group and the like.

The aromatic hydrocarbon group includes, for example, aryl groups suchas a phenyl group, a naphthyl group, an anthryl group, a biphenyl groupand a phenanthryl group. The aromatic hydrocarbon group may have a chainhydrocarbon group or an alicyclic hydrocarbon group and examples thereofinclude an aromatic hydrocarbon group having a chain hydrocarbon group(a tolyl group, a xylyl group, a cumenyl group, a mesityl group, ap-methylphenyl group, a p-ethylphenyl group, a p-tert-butylphenyl group,a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.) and anaromatic hydrocarbon group having alicyclic hydrocarbon group (ap-cyclohexylphenyl group, a p-adamantylphenyl group, etc.).

The alkyl group includes, for example, a methyl group, an ethyl group, apropyl group, an isopropyl group, a butyl group, a sec-butyl group, atert-butyl group, a pentyl group, a hexyl group, a heptyl group, a2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, anundecyl group, a dodecyl group and the like.

Examples of the alkyl group substituted with a hydroxy group includehydroxyalkyl groups such as a hydroxymethyl group and a hydroxyethylgroup.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, aheptyloxy group, an octyloxy group, a decyloxy group and a dodecyloxygroup.

Examples of the aralkyl group include a benzyl group, a phenethyl group,a phenylpropyl group, a naphthylmethyl group and a naphthylethyl group.

The alkylcarbonyl group includes, for example, an acetyl group, apropionyl group and a butyryl group.

Examples of Y include the followings.

Y is preferably an alicyclic hydrocarbon group having 3 to 18 carbonatoms which may have a substituent, more preferably an adamantyl groupwhich may have a substituent, and —CH₂— constituting the alicyclichydrocarbon group or the adamantyl group may be replaced by —CO—,—S(O)₂— or —CO—. Y is still more preferably an adamantyl group, ahydroxyadamantyl group, an oxoadamantyl group, or groups represented bythe following formulas.

The sulfonic acid anion in the salt represented by formula (B1) ispreferably anions represented by formula (B1-A-1) to formula (B1-A-55)[hereinafter sometimes referred to as “anion (B1-A-1)” according to thenumber of formula], and more preferably an anion represented by any oneof formula (B1-A-1) to formula (B1-A-4), formula (B1-A-9), formula(B1-A-10), formula (B1-A-24) to formula (B1-A-33), formula (B1-A-36) toformula (B1-A-40) and formula (B1-A-47) to formula (B1-A-55).

R^(i2) to R^(i7) each independently represent, for example, an alkylgroup having 1 to 4 carbon atoms, and preferably a methyl group or anethyl group. R^(i8) is, for example, a chain hydrocarbon group having 1to 12 carbon atoms, preferably an alkyl group having 1 to 4 carbonatoms, an alicyclic hydrocarbon group having 5 to 12 carbon atoms orgroups formed by combining these groups, and more preferably a methylgroup, an ethyl group, a cyclohexyl group or an adamantyl group. L^(A41)is a single bond or an alkanediyl group having 1 to 4 carbon atoms.

Q^(b1) and Q^(b2) are the same as defined above.

Specific examples of the sulfonic acid anion in the salt represented byformula (B1) include anions mentioned in JP 2010-204646 A.

Examples of sulfonic acid anion in the salt represented by formula (B1)are preferably anions represented by formula (B1a-1) to formula(B1a-34).

Of these, an anion represented by any one of formula (B1a-1) to formula(B1a-3) and formula (B1a-7) to formula (B1a-16), formula (B1a-18),formula (B1a-19) and formula (B1a-22) to formula (B1a-34) is preferable.

Examples of the organic cation of Z1⁺ include an organic onium cation,an organic sulfonium cation, an organic iodonium cation, an organicammonium cation, a benzothiazolium cation and an organic phosphoniumcation. Of these, an organic sulfonium cation and an organic iodoniumcation are preferable, and an arylsulfonium cation is more preferable.Specific examples thereof include a cation represented by any one offormula (b2-1) to formula (b2-4) (hereinafter sometimes referred to as“cation (b2-1)” according to the number of formula).

In formula (b2-1) to formula (b2-4), R^(b4) to R^(b6) each independentlyrepresent an aliphatic hydrocarbon group having 1 to 30 carbon atoms, analicyclic hydrocarbon group having 3 to 36 carbon atoms or an aromatichydrocarbon group having 6 to 36 carbon atoms, a hydrogen atom includedin the aliphatic hydrocarbon group may be substituted with a hydroxygroup, an alkoxy group having 1 to 12 carbon atoms, an alicyclichydrocarbon group having 3 to 12 carbon atoms or an aromatic hydrocarbongroup having 6 to 18 carbon atoms, a hydrogen atom included in thealicyclic hydrocarbon group may be substituted with a halogen atom, analiphatic hydrocarbon group having 1 to 18 carbon atoms, analkylcarbonyl group having 2 to 4 carbon atoms or a glycidyloxy group,and a hydrogen atom included in the aromatic hydrocarbon group may besubstituted with a halogen atom, a hydroxy group or an alkoxy grouphaving 1 to 12 carbon atoms,

R^(b4) and R^(b5) may be bonded to each other to form a ring togetherwith sulfur atoms to which R^(b4) and R^(b5) are bonded, and —CH₂—included in the ring may be replaced by —O—, —S— or —CO—,

R^(b7) and R^(b8) each independently represent a hydroxy group, analiphatic hydrocarbon group having 1 to 12 carbon atoms or an alkoxygroup having 1 to 12 carbon atoms,

m2 and n2 each independently represent an integer of 0 to 5,

when m2 is 2 or more, a plurality of R^(b7) may be the same ordifferent, and when n2 is 2 or more, a plurality of R^(b8) may be thesame or different,

R^(b9) and R^(b10) each independently represent an aliphatic hydrocarbongroup having 1 to 36 carbon atoms or an alicyclic hydrocarbon grouphaving 3 to 36 carbon atoms,

R^(b9) and R^(b10) may be bonded to each other to form a ring togetherwith sulfur atoms to which R^(b9) and R^(b10) are bonded, and —CH₂—included in the ring may be replaced by —O—, —S— or —CO—,

R^(b11) represents a hydrogen atom, an aliphatic hydrocarbon grouphaving 1 to 36 carbon atoms, an alicyclic hydrocarbon group having 3 to36 carbon atoms or an aromatic hydrocarbon group having 6 to 18 carbonatoms,

R^(b12) represents an aliphatic hydrocarbon group having 1 to 12 carbonatoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms or anaromatic hydrocarbon group having 6 to 18 carbon atoms, a hydrogen atomincluded in the aliphatic hydrocarbon may be substituted with anaromatic hydrocarbon group having 6 to 18 carbon atoms, and a hydrogenatom included in the aromatic hydrocarbon group may be substituted withan alkoxy group having 1 to 12 carbon atoms or an alkylcarbonyloxy grouphaving 1 to 12 carbon atoms,

R^(b11) and R^(b12) may be bonded to each other to form a ring,including —CH—CO— to which R^(b11) and R^(b12) are bonded, and —CH₂—included in the ring may be replaced by —O—, —S— or —CO—,

R^(b13) to R^(b18) each independently represent a hydroxy group, analiphatic hydrocarbon group having 1 to 12 carbon atoms or an alkoxygroup having 1 to 12 carbon atoms,

L^(b31) represents a sulfur atom or an oxygen atom,

o2, p2, s2 and t2 each independently represent an integer of 0 to 5,

q2 and r2 each independently represent an integer of 0 to 4,

u2 represents 0 or 1, and

when o2 is 2 or more, a plurality of R^(b13) are the same or differentfrom each other, when p2 is 2 or more, a plurality of R^(b14) are thesame or different from each other, when q2 is 2 or more, a plurality ofR^(b15) are the same or different from each other, when r2 is 2 or more,a plurality of R^(b16) are the same or different from each other, whens2 is 2 or more, a plurality of R^(b17) are the same or different fromeach other, and when t2 is 2 or more, a plurality of R^(b18) are thesame or different from each other.

Examples of the aliphatic hydrocarbon group include alkyl groups such asa methyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, ahexyl group, an octyl group and a 2-ethylhexyl group. Particularly, thealiphatic hydrocarbon group of R^(b9) to R^(b12) preferably has 1 to 12carbon atoms.

The alicyclic hydrocarbon group may be either monocyclic or polycyclic,and examples of the monocyclic alicyclic hydrocarbon group includecycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, acyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctylgroup and a cyclodecyl group. Examples of the polycyclic alicyclichydrocarbon group include a decahydronaphthyl group, an adamantyl group,a norbornyl group and the following groups.

Particularly, the alicyclic hydrocarbon group of R^(b9) to R^(b12)preferably has 3 to 18 carbon atoms, and more preferably 4 to 12 carbonatoms.

Examples of the alicyclic hydrocarbon group in which a hydrogen atom issubstituted with an aliphatic hydrocarbon group include amethylcyclohexyl group, a dimethylcyclohexyl group, a2-methyladamantan-2-yl group, a 2-ethyladamantan-2-yl group, a2-isopropyladamantan-2-yl group, a methylnorbornyl group, an isobornylgroup and the like. In the alicyclic hydrocarbon group in which ahydrogen atom is substituted with an aliphatic hydrocarbon group, thetotal number of carbon atoms of the alicyclic hydrocarbon group and thealiphatic hydrocarbon group is preferably 20 or less.

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a biphenyl group, a naphthyl group, a phenanthryl groupand the like. The aromatic hydrocarbon group may have a chainhydrocarbon group or an alicyclic hydrocarbon group and examples thereofinclude an aromatic hydrocarbon group having a chain hydrocarbon grouphaving 1 to 18 carbon atoms (a tolyl group, a xylyl group, a cumenylgroup, a mesityl group, a p-methylphenyl group, a p-ethylphenyl group, ap-tert-butylphenyl group, a 2,6-diethylphenyl group, a2-methyl-6-ethylphenyl group, etc.) and an aromatic hydrocarbon grouphaving alicyclic hydrocarbon group having 3 to 18 carbon atoms (ap-cyclohexylphenyl group, a p-adamantylphenyl group, etc.).

Examples of the aromatic hydrocarbon group in which a hydrogen atom issubstituted with an alkoxy group include a p-methoxyphenyl group and thelike.

Examples of the aliphatic hydrocarbon group in which a hydrogen atom issubstituted with an aromatic hydrocarbon group include aralkyl groupssuch as a benzyl group, a phenethyl group, a phenylpropyl group, atrityl group, a naphthylmethyl group and a naphthylethyl group.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, aheptyloxy group, an octyloxy group, a decyloxy group and a dodecyloxygroup.

Examples of the alkylcarbonyl group include an acetyl group, a propionylgroup and a butyryl group.

Examples of the halogen atom include a fluorine atom, a chlorine atom, abromine atom and an iodine atom.

Examples of the alkylcarbonyloxy group include a methylcarbonyloxygroup, an ethylcarbonyloxy group, a propylcarbonyloxy group, anisopropylcarbonyloxy group, a butylcarbonyloxy group, asec-butylcarbonyloxy group, a tert-butylcarbonyloxy group, apentylcarbonyloxy group, a hexylcarbonyloxy group, an octylcarbonyloxygroup and a 2-ethylhexylcarbonyloxy group.

The ring formed by bonding R^(b4) and R^(b5) each other, together withsulfur atoms to which R^(b4) and R^(b5) are bonded, may be a monocyclic,polycyclic, aromatic, nonaromatic, saturated or unsaturated ring. Thisring includes a ring having 3 to 18 carbon atoms and is preferably aring having 4 to 18 carbon atoms. The ring containing a sulfur atomincludes a 3-membered to 12-membered ring and is preferably a 3-memberedto 7-membered ring and includes, for example, the following rings. *represents a bonding site.

The ring formed by combining R^(b9) and R^(b10) together may be amonocyclic, polycyclic, aromatic, nonaromatic, saturated or unsaturatedring. This ring includes a 3-membered to 12-membered ring and ispreferably a 3-membered to 7-membered ring. The ring includes, forexample, a thiolan-1-ium ring (tetrahydrothiophenium ring), athian-1-ium ring, a 1,4-oxathian-4-ium ring and the like.

The ring formed by combining R^(b11) and R^(b12) together may be amonocyclic, polycyclic, aromatic, nonaromatic, saturated or unsaturatedring. This ring includes a 3-membered to 12-membered ring and ispreferably a 3-membered to 7-membered ring. Examples thereof include anoxocycloheptane ring, an oxocyclohexane ring, an oxonorbornane ring, anoxoadamantane ring and the like.

Of cation (b2-1) to cation (b2-4), a cation (b2-1) is preferable.

Examples of the cation (b2-1) include the following cations.

Examples of the cation (b2-2) include the following cations.

Examples of the cation (b2-3) include the following cations.

Examples of the cation (b2-4) include the following cations.

The acid generator (B) is a combination of the sulfonic acid anionmentioned above and the organic cation mentioned above, and these can beoptionally combined. The acid generator (B) preferably includes acombination of an anion represented by any one of formula (B1a-1) toformula (B1a-3), formula (B1a-7) to formula (B1a-16), formula (B1a-18),formula (B1a-19) and formula (B1a-22) to formula (B1a-34) and a cation(b2-1) or a cation (b2-3).

The acid generator (B) preferably includes those represented by formula(B1-1) to formula (B1-48). Of these acid generators, those containing anarylsulfonium cation are preferable and those represented by formula(B1-1) to formula (B1-3), formula (B1-5) to formula (B1-7), formula(B1-11) to formula (B1-14), formula (B1-20) to formula (B1-26), formula(B1-29) and formula (B1-31) to formula (B1-48) are particularlypreferable.

In the resist composition of the present invention, the content of theacid generator is preferably 1 part by mass or more and 40 parts by massor less, more preferably 3 parts by mass or more and 35 parts by mass orless, and still more preferably 10 parts by mass or more and 35 parts bymass or less, based on 100 parts by mass of the below-mentioned resin(A).

When the salt (I) and the acid generator (B) are included as the acidgenerator, a ratio of the content of the salt (I) and that of the acidgenerator (B) (mass ratio; salt (I):acid generator (B)) is usually 1:99to 99:1, preferably 2:98 to 98:2, more preferably 5:95 to 95:5, stillmore preferably 10:90 to 90:10, and particularly preferably 15:85 to85:15.

<Resist Composition>

The resist composition of the present invention includes an acidgenerator including a salt (I) and a resin having an acid-labile group(hereinafter sometimes referred to as “resin (A)”). The “acid-labilegroup” means a group having a leaving group which is eliminated bycontact with an acid, thus converting a constitutional unit into aconstitutional unit having a hydrophilic group (e.g. a hydroxy group ora carboxy group).

The resist composition of the present invention preferably includes aquencher such as a salt generating an acid having an acidity lower thanthat of an acid generated from the acid generator (hereinafter sometimesreferred to as “quencher (C)”), and preferably includes a solvent(hereinafter sometimes referred to as “solvent (E)”).

<Resin (A)>

The resin (A) includes a structural unit having an acid-labile group(hereinafter sometimes referred to as “structural unit (a1)”). It ispreferable that the resin (A) further includes a structural unit otherthan the structural unit (a1). Examples of the structural unit otherthan the structural unit (a1) include a structural unit having noacid-labile group (hereinafter sometimes referred to as “structural unit(s)”), a structural unit other than the structural unit (a1) and thestructural unit (s) (e.g. a structural unit having a halogen atommentioned later (hereinafter sometimes referred to as “structural unit(a4)”), a structural unit having a non-leaving hydrocarbon groupmentioned later (hereinafter sometimes referred to as “structural unit(a5))) and other structural units derived from monomers known in theart.

<Structural Unit (a1)>

The structural unit (a1) is derived from a monomer having an acid-labilegroup (hereinafter sometimes referred to as “monomer (a1)”).

The acid-labile group contained in the resin (A) is preferably a grouprepresented by formula (1) (hereinafter also referred to as group (1))and/or a group represented by formula (2) (hereinafter also referred toas group (2)):

wherein, in formula (1), R^(a)i, R^(a2) and R^(a3) each independentlyrepresent an alkyl group having 1 to 8 carbon atoms, an alicyclichydrocarbon group having 3 to 20 carbon atoms or groups obtained bycombining these groups, or R^(a1) and R^(a2) are bonded to each other toform a nonaromatic hydrocarbon ring having 3 to 20 carbon atoms togetherwith carbon atoms to which R^(a1) and R^(a2) are bonded,

ma and na each independently represent 0 or 1, and at least one of maand na represents 1, and

* represents a bonding site:

wherein, in formula (2), R^(a1′) and R^(a2′) each independentlyrepresent a hydrogen atom or a hydrocarbon group having 1 to 12 carbonatoms, R^(a3′) represents a hydrocarbon group having 1 to 20 carbonatoms, or R^(a2′) and R^(a3′) are bonded to each other to form aheterocyclic ring having 3 to 20 carbon atoms together with carbon atomsand X to which R^(a2′) and R^(a3′) are bonded, and —CH₂— included in thehydrocarbon group and the heterocyclic ring may be replaced by —O— or—S—,

X represents an oxygen atom or a sulfur atom,

na′ represents 0 or 1, and

* represents a bonding site.

Examples of the alkyl group in R^(a1), R^(a2) and R^(a3) include amethyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, a hexyl group, a heptyl group, an octyl group and the like.

The alicyclic hydrocarbon group in R^(a1), R^(a2) and R^(a3) may beeither monocyclic or polycyclic. Examples of the monocyclic alicyclichydrocarbon group include cycloalkyl groups such as a cyclopentyl group,a cyclohexyl group, a cycloheptyl group and a cyclooctyl group. Examplesof the polycyclic alicyclic hydrocarbon group include adecahydronaphthyl group, an adamantyl group, a norbornyl group and thefollowing groups (* represents a bonding site). The number of carbonatoms of the alicyclic hydrocarbon group of R^(a1), R^(a2) and R^(a) ispreferably 3 to 16.

The group obtained by combining an alkyl group with an alicyclichydrocarbon group includes, a for example, a methylcyclohexyl group, adimethylcyclohexyl group, a methylnorbornyl group, a cyclohexylmethylgroup, an adamantylmethyl group, an adamantyldimethyl group, anorbornylethyl group and the like.

Preferably, ma is 0 and na is 1.

When R^(a1) and R^(a2) are bonded to each other to form a nonaromatichydrocarbon ring, examples of —C(R^(a1))(R^(a2))(R^(a3)) include thefollowing rings. The nonaromatic hydrocarbon ring preferably has 3 to 12carbon atoms. * represents a bonding site to —O—.

Examples of the hydrocarbon group in R^(a1′), R^(a2′) and R^(a3′)include an alkyl group, an alicyclic hydrocarbon group, an aromatichydrocarbon group and groups obtained by combining these groups.

Examples of the alkyl group and the alicyclic hydrocarbon group includethose which are the same as mentioned in R^(a1), R^(a2) and R^(a3).

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a naphthyl group, an anthryl group, a biphenyl group and aphenanthryl group.

Examples of the group combined include a group obtained by combining theabove-mentioned alkyl group and alicyclic hydrocarbon group (e.g., acycloalkylalkyl group), an aralkyl group such as a benzyl group, anaromatic hydrocarbon group having an alkyl group (a p-methylphenylgroup, a p-tert-butylphenyl group, a tolyl group, a xylyl group, acumenyl group, a mesityl group, a 2,6-diethylphenyl group, a2-methyl-6-ethylphenyl group, etc.), an aromatic hydrocarbon grouphaving an alicyclic hydrocarbon group (a p-cyclohexylphenyl group, ap-adamantylphenyl group, etc.), an aryl-cycloalkyl group (aphenylcyclohexyl group, etc.), and the like.

When R^(a2′) and R^(a3′) are bonded to each other to form a heterocyclicring together with carbon atoms and X to which R^(a2′) and R^(a3′) arebonded, examples of —C(R^(a1′))(R^(a3′))—X—R^(a2′) include the followingrings. * represents a bonding site.

Of R^(a1′) and R^(a2′), at least one is preferably a hydrogen atom.

na′ is preferably 0.

Examples of the group (1) include the following groups.

A group wherein, in formula (1), R^(a1), R^(a2) and R^(a3) are alkylgroups, ma=0 and na=1. The group is preferably a tert-butoxycarbonylgroup.

A group wherein, in formula (1), R^(a1) and R^(a2) are bonded to eachother to form an adamantyl group together with carbon atoms to whichR^(a1) and R^(a2) are bonded, R^(a3) is an alkyl group, ma=0 and na=1.

A group wherein, in formula (1), R^(a1) and R^(a2) are eachindependently an alkyl group, R^(a3) is an adamantyl group, ma=0 andna=1.

Specific examples of the group (1) include the following groups. *represents a bonding site.

Specific examples of the group (2) include the following groups. *represents a bonding site.

The monomer (a1) is preferably a monomer having an acid-labile group andan ethylenic unsaturated bond, and more preferably a (meth)acrylicmonomer having an acid-labile group.

Of the (meth)acrylic monomers having an acid-labile group, those havingan alicyclic hydrocarbon group having 5 to 20 carbon atoms arepreferably exemplified. When a resin (A) including a structural unitderived from a monomer (a1) having a bulky structure such as analicyclic hydrocarbon group is used in a resist composition, it ispossible to improve the resolution of a resist pattern.

The structural unit derived from a (meth)acrylic monomer having a group(1) includes a structural unit represented by formula (a1-0)(hereinafter sometimes referred to as structural unit (a1-0)), astructural unit represented by formula (a1-1) (hereinafter sometimesreferred to as structural unit (a1-1)) or a structural unit representedby formula (a1-2) (hereinafter sometimes referred to as structural unit(a1-2)). At least one selected from the group consisting of a structuralunit (a1-1) and a structural unit (a1-2) is preferable. These structuralunits may be used alone, or two or more structural units may be used incombination.

In formula (a1-0), formula (a1-1) and formula (a1-2),

L^(a01), L^(a1) and L^(a2) each independently represent —O— or*—O—(CH₂)_(k1)—CO—O—, k1 represents an integer of 1 to 7, and *represents a bonding site to —CO—,

R^(a01), R^(a)a and R^(a5) each independently represent a hydrogen atomor a methyl group,

R^(a02), R^(a03) and R^(a04) each independently represent an alkyl grouphaving 1 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to18 carbon atoms or groups obtained by combining these groups,

R^(a6) and R^(a7) each independently represent an alkyl group having 1to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms or groups obtained by combining these groups,

m1 represents an integer of 0 to 14,

n1 represents an integer of 0 to 10, and

n1′ represents an integer of 0 to 3.

R^(a01), R^(a4) and R^(a5) are preferably a methyl group.

L^(a01), L^(a1) and L^(a2) are preferably an oxygen atom or*—O—(CH₂)_(k01)—CO—O— (in which k01 is preferably an integer of 1 to 4,and more preferably 1), and more preferably an oxygen atom.

Examples of the alkyl group, the alicyclic hydrocarbon group and groupsobtained by combining these groups in R^(a02), R^(a03), R^(a04), R^(a6)and R^(a7) include the same groups as mentioned for R^(a1), R^(a2) andR^(a3) of formula (1).

The alkyl group in R^(a02), R^(a03) and R^(a04) is preferably an alkylgroup having 1 to 6 carbon atoms, more preferably a methyl group or anethyl group, and still more preferably a methyl group.

The alkyl group in R^(a6) and R^(a7) is preferably an alkyl group having1 to 6 carbon atoms, more preferably a methyl group, an ethyl group oran isopropyl group, and still more preferably an ethyl group or anisopropyl group.

The number of carbon atoms of the alicyclic hydrocarbon group ofR^(a)o2, R^(a03), R^(a04), R^(a6) and R^(a) is preferably 5 to 12, andmore preferably 5 to 10.

The total number of carbon atoms of the group obtained by combining thealkyl group with the alicyclic hydrocarbon group is preferably 18 orless.

R^(a02) and R^(a03) are preferably an alkyl group having 1 to 6 carbonatoms, and more preferably a methyl group or an ethyl group.

R^(a04) is preferably an alkyl group having 1 to 6 carbon atoms or analicyclic hydrocarbon group having 5 to 12 carbon atoms, and morepreferably a methyl group, an ethyl group, a cyclohexyl group or anadamantyl group.

Preferably, R^(a6) and R^(a7) are each independently an alkyl grouphaving 1 to 6 carbon atoms, more preferably a methyl group, an ethylgroup or an isopropyl group, and still more preferably an ethyl group oran isopropyl group.

m1 is preferably an integer of 0 to 3, and more preferably 0 or 1.

n1 is preferably an integer of 0 to 3, and more preferably 0 or 1.

n1′ is preferably 0 or 1.

The structural unit (a1-0) includes, for example, a structural unitrepresented by any one of formula (a1-0-1) to formula (a1-0-12) and astructural unit in which a methyl group corresponding to R^(a01) in thestructural unit (a1-0) is substituted with a hydrogen atom and ispreferably a structural unit represented by any one of formula (a1-0-1)to formula (a1-0-10).

The structural unit (a1-1) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-204646 A. Of thesestructural units, a structural unit represented by any one of formula(a1-1-1) to formula (a1-1-4) and a structural unit in which a methylgroup corresponding to R^(a4) in the structural unit (a1-1) issubstituted with a hydrogen atom are preferable, and a structural unitrepresented by any one of formula (a1-1-1) to formula (a1-1-4) is morepreferable.

Examples of the structural unit (a1-2) include a structural unitrepresented by any one of formula (a1-2-1) to formula (a1-2-6) and astructural unit in which a methyl group corresponding to R^(as) in thestructural unit (a1-2) is substituted with a hydrogen atom, andstructural units represented by formula (a1-2-2), formula (a1-2-5) andformula (a1-2-6) are preferable.

When the resin (A) includes a structural unit (a1-0), the total contentthereof is usually 1 to 60 mol %, preferably 3 to 50 mol %, and morepreferably 5 to 40 mol % based on all structural units of the resin (A).

When the resin (A) includes a structural unit (a1-1) and/or a structuralunit (a1-2), the total content thereof is usually 10 to 95 mol %,preferably 15 to 90 mol %, more preferably 15 to 85 mol %, still morepreferably 20 to 75 mol %, and yet more preferably 20 to 70 mol %, basedon all structural units of the resin (A).

In the structural unit (a1), examples of the structural unit having agroup (2) include a structural unit represented by formula (a1-4)(hereinafter sometimes referred to as “structural unit (a1-4)”):

wherein, in formula (a1-4),

R^(a32) represents a hydrogen atom, a halogen atom or an alkyl grouphaving 1 to 6 carbon atoms which may have a halogen atom,

R^(a33) represents a halogen atom, a hydroxy group, an alkyl grouphaving 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms,an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxygroup having 2 to 4 carbon atoms, an acryloyloxy group or amethacryloyloxy group.

la represents an integer of 0 to 4, and when la is 2 or more, aplurality of R^(a33) may be the same or different from each other, and

R^(a34) and R^(a35) each independently represent a hydrogen atom or ahydrocarbon group having 1 to 12 carbon atoms, R^(a36) represents ahydrocarbon group having 1 to 20 carbon atoms, or R^(a35) and R^(a36)are bonded to each other to form a divalent hydrocarbon group having 2to 20 carbon atoms together with —C—O— to which R^(a33) and R^(a36) arebonded, and —CH₂— included in the hydrocarbon group and the divalenthydrocarbon group may be replaced by —O— or —S—.

Examples of the alkyl group in R^(a32) and R^(a33) include a methylgroup, an ethyl group, a propyl group, an isopropyl group, a butylgroup, a pentyl group and a hexyl group. The alkyl group is preferablyan alkyl group having 1 to 4 carbon atoms, more preferably a methylgroup or an ethyl group, and still more preferably a methyl group.

Examples of the halogen atom in R^(a32) and R^(a33) include a fluorineatom, a chlorine atom and a bromine atom.

Examples of the alkyl group having 1 to 6 carbon atoms which may have ahalogen atom include a trifluoromethyl group, a difluoromethyl group, amethyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group,a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutylgroup, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, aperfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, apentyl group, a hexyl group, a perfluorohexyl group and the like.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentyloxy group and a hexyloxy group.Of these groups, an alkoxy group having 1 to 4 carbon atoms ispreferable, a methoxy group or an ethoxy group are more preferable, anda methoxy group is still more preferable.

Examples of the alkylcarbonyl group include an acetyl group, a propionylgroup and a butyryl group.

Examples of the alkylcarbonyloxy group include an acetyloxy group, apropionyloxy group, a butyryloxy group and the like.

Examples of the hydrocarbon group in R^(a34), R^(a35) and R^(a36)include an alkyl group, an alicyclic hydrocarbon group, an aromatichydrocarbon group and groups obtained by combining these groups.

Examples of the alkyl group include a methyl group, an ethyl group, apropyl group, a butyl group, a pentyl group, a hexyl group, a heptylgroup, an octyl group and the like.

The alicyclic hydrocarbon group may be either monocyclic or polycyclic,and examples of the monocyclic alicyclic hydrocarbon group includecycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, acycloheptyl group and a cyclooctyl group. Examples of the polycyclicalicyclic hydrocarbon group include a decahydronaphthyl group, anadamantyl group, a norbornyl group and the following groups (*represents a bonding site).

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a naphthyl group, an anthryl group, a biphenyl group and aphenanthryl group.

Examples of the combined group include a group obtained by combining theabove-mentioned alkyl group and alicyclic hydrocarbon group, an aralkylgroup such as a benzyl group, an aromatic hydrocarbon group having analkyl group (a p-methylphenyl group, a p-tert-butylphenyl group, a tolylgroup, a xylyl group, a cumenyl group, a mesityl group, a2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), anaromatic hydrocarbon group having an alicyclic hydrocarbon group (ap-cyclohexylphenyl group, a p-adamantylphenyl group, etc.), anaryl-cyclohexyl group such as a phenylcyclohexyl group and the like.Particularly, examples of R^(a36) include an alkyl group having 1 to 18carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms orgroups obtained by combining these groups.

In formula (a1-4), R^(a32) is preferably a hydrogen atom,

R^(a33) is preferably an alkoxy group having 1 to 4 carbon atoms, morepreferably a methoxy group and an ethoxy group, and still morepreferably a methoxy group,

la is preferably 0 or 1, and more preferably 0,

R^(a34) is preferably a hydrogen atom, and

R^(a35) is preferably an alkyl group having 1 to 12 carbon atoms or analicyclic hydrocarbon group, and more preferably a methyl group or anethyl group.

The hydrocarbon group of R^(a36) is preferably an alkyl group having 1to 18 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms orgroups formed by combining these groups, and more preferably an alkylgroup having 1 to 18 carbon atoms, an alicyclic aliphatic hydrocarbongroup having 3 to 18 carbon atoms or an aralkyl group having 7 to 18carbon atoms. The alkyl group and the alicyclic hydrocarbon group inR^(a36) are preferably unsubstituted. The aromatic hydrocarbon group inR^(a36) is preferably an aromatic ring having an aryloxy group having 6to 10 carbon atoms.

—OC(R^(a34))(R^(a35))—O—R^(a36) in the structural unit (a1-4) iseliminated by contacting with an acid (e.g., p-toluenesulfonic acid) toform a hydroxy group.

The structural unit (a1-4) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-204646 A. The structuralunit preferably includes structural units represented by formula(a1-4-1) to formula (a1-4-12) and a structural unit in which a hydrogenatom corresponding to R^(a32) in the constitutional unit (a1-4) issubstituted with a methyl group, and more preferably structural unitsrepresented by formula (a1-4-1) to formula (a1-4-5) and formula(a1-4-10).

When the resin (A) includes the structural unit (a1-4), the content ispreferably 10 to 95 mol %, more preferably 15 to 90 mol %, still morepreferably 20 to 85 mol %, yet more preferably 20 to 70 mol %, andparticularly preferably 20 to 60 mol %, based on the total of allstructural units of the resin (A).

The structural unit derived from a (meth)acrylic monomer having a group(2) also includes a structural unit represented by formula (a1-5)(hereinafter sometimes referred to as “structural unit (a1-5)”).

In formula (a1-5),

R^(a8) represents an alkyl group having 1 to 6 carbon atoms which mayhave a halogen atom, a hydrogen atom or a halogen atom,

Z^(a1) represents a single bond or *—(CH₂)_(h3)—CO-L⁵⁴-, h3 representsan integer of 1 to 4, and * represents a bonding site to L⁵¹,

L⁵¹, L⁵², L⁵³ and L⁵⁴ each independently represent —O— or —S—,

s1 represents an integer of 1 to 3, and

s1′ represents an integer of 0 to 3.

The halogen atom includes a fluorine atom and a chlorine atom and ispreferably a fluorine atom. Examples of the alkyl group having 1 to 6carbon atoms which may have a halogen atom include a methyl group, anethyl group, a propyl group, a butyl group, a pentyl group, a hexylgroup, a heptyl group, an octyl group, a fluoromethyl group and atrifluoromethyl group.

In formula (a1-5), R^(a8) is preferably a hydrogen atom, a methyl groupor a trifluoromethyl group,

L⁵¹ is preferably an oxygen atom,

one of L⁵² and L⁵³ is preferably —O— and the other one is preferably—S—,

s1 is preferably 1,

s1′ is preferably an integer of 0 to 2, and

Z^(a1) is preferably a single bond or *—CH₂—CO—O—.

The structural unit (a1-5) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-61117 A. Of thesestructural units, structural units represented by formula (a1-5-1) toformula (a1-5-4) are preferable, and structural units represented byformula (a1-5-1) or formula (a1-5-2) are more preferable.

When the resin (A) includes the structural unit (a1-5), the content ispreferably 1 to 50 mol %, more preferably 3 to 45 mol %, still morepreferably 5 to 40 mol %, and yet more preferably 5 to 30 mol %, basedon all structural units of the resin (A).

The structural unit (a1) also includes the following structural units.

When the resin (A) includes the above-mentioned structural units such as(a1-3-1) to (a1-3-7), the content is preferably 10 to 95 mol %, morepreferably 15 to 90 mol %, still more preferably 20 to 85 mol %, yetmore preferably 20 to 70 mol %, and particularly preferably 20 to 60 mol%, based on all structural units of the resin (A).

<Structural Unit (s)>

The structural unit (s) is derived from a monomer having no acid-labilegroup (hereinafter sometimes referred to as “monomer (s)”). It ispossible to use, as the monomer from which the structural unit (s) isderived, a monomer having no acid-labile group known in the resistfield.

The structural unit (s) preferably has a hydroxy group or a lactonering. When a resin including a structural unit having a hydroxy groupand having no acid-labile group (hereinafter sometimes referred to as“structural unit (a2)”) and/or a structural unit having a lactone ringand having no acid-labile group (hereinafter sometimes referred to as“structural unit (a3)”) is used in the resist composition of the presentinvention, it is possible to improve the resolution of a resist patternand the adhesion to a substrate.

<Structural Unit (a2)>

The hydroxy group possessed by the structural unit (a2) may be either analcoholic hydroxy group or a phenolic hydroxy group.

When a resist pattern is produced from the resist composition of thepresent invention, in the case of using, as an exposure source, highenergy rays such as KrF excimer laser (248 nm), electron beam or extremeultraviolet light (EUV), it is preferable to use a structural unit (a2)having a phenolic hydroxy group as the structural unit (a2). When usingArF excimer laser (193 nm) or the like, a structural unit (a2) having analcoholic hydroxy group is preferably used as the structural unit (a2),and it is more preferably use the below-mentioned structural unit (a2-1)or structural unit (a2-A). The structural unit (a2) may be includedalone, or two or more structural units may be included.

In the structural unit (a2), examples of the structural unit having aphenolic hydroxy group include a structural unit represented by formula(a2-A) (hereinafter sometimes referred to as “structural unit (a2-A)”)

wherein, in formula (a2-A),

R^(a50) represents a hydrogen atom, a halogen atom or an alkyl grouphaving 1 to 6 carbon atoms which may have a halogen atom,

R^(a51) represents a halogen atom, a hydroxy group, an alkyl grouphaving 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms,an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxygroup having 2 to 4 carbon atoms, an acryloyloxy group or amethacryloyloxy group,

A^(a50) represents a single bond or *—X^(a51)-(A^(a52)-X^(a52))_(nb)—,and * represents a bonding site to carbon atoms to which —R^(a50) isbonded,

A^(a52) represents an alkanediyl group having 1 to 6 carbon atoms,

X^(a51) and X^(a52) each independently represent —O—, —CO—O— or —O—CO—,

nb represents 0 or 1, and

mb represents an integer of 0 to 4, and when mb is an integer of 2 ormore, a plurality of R^(a51) may be the same or different from eachother.

Examples of the halogen atom in R^(a50) include a fluorine atom, achlorine atom and a bromine atom.

Examples of the alkyl group having 1 to 6 carbon atoms which may have ahalogen atom in R^(a50) include a trifluoromethyl group, adifluoromethyl group, a methyl group, a perfluoroethyl group, a2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethylgroup, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, apropyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutylgroup, a butyl group, a perfluoropentyl group, a2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl groupand a perfluorohexyl group.

R^(a50) is preferably a hydrogen atom or an alkyl group having 1 to 4carbon atoms, more preferably a hydrogen atom, a methyl group or anethyl group, and still more preferably a hydrogen atom or a methylgroup.

Examples of the alkyl group in R^(a51) include a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, a sec-butylgroup, a tert-butyl group, a pentyl group and a hexyl group.

Examples of the alkoxy group in R^(a51) include a methoxy group, anethoxy group, a propoxy group, an isopropoxy group, a butoxy group, asec-butoxy group and a tert-butoxy group. An alkoxy group having 1 to 4carbon atoms is preferable, a methoxy group or an ethoxy group is morepreferable, and a methoxy group is still more preferable.

Examples of the alkylcarbonyl group in R^(a51) include an acetyl group,a propionyl group and a butyryl group.

Examples of the alkylcarbonyloxy group in R^(as)51 include an acetyloxygroup, a propionyloxy group and a butyryloxy group.

R^(a51) is preferably a methyl group.

Examples of *—X^(a51)-(A^(a52)-X^(a52))_(nb)— include *—O—, *—CO—O—,*—O—CO—, *—CO—O-A^(a52)-CO—O—, *—O—CO-A^(a52)-O—, *—O-A^(a52)-CO—O—,*—CO—O-A^(a52)-O—CO— and *—O—CO-A^(a52)-O—CO—. Of these, *—CO—O—,*—CO—O-A^(a52)-CO—O— or *—O-A^(a52)-CO—O— is preferable.

Examples of the alkanediyl group include a methylene group, an ethylenegroup, a propane-1,3-diyl group, a propane-1,2-diyl group, abutane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diylgroup, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a2-methylbutane-1,4-diyl group.

A^(a52) is preferably a methylene group or an ethylene group.

A^(a50) is preferably a single bond, *—CO—O— or *—CO—O-A^(a52)-CO—O—,more preferably a single bond, *—CO—O— or *—CO—O—CH₂—CO—O—, and stillmore preferably a single bond or *—CO—O—.

mb is preferably 0, 1 or 2, more preferably 0 or 1, and particularlypreferably 0.

The hydroxy group is preferably bonded to the o-position or thep-position of a benzene ring, and more preferably the p-position.

Examples of the structural unit (a2-A) include structural units derivedfrom the monomers mentioned in JP 2010-204634 A and JP 2012-12577 A.

Examples of the structural unit (a2-A) include structural unitsrepresented by formula (a2-2-1) to formula (a2-2-6), and a structuralunit in which a methyl group corresponding to R^(a50) in the structuralunit (a2-A) is substituted with a hydrogen atom in structural unitsrepresented by formula (a2-2-1) to formula (a2-2-6). The structural unit(a2-A) is preferably a structural unit in which a methyl groupcorresponding to R^(a50) in the structural unit (a2-A) is substitutedwith a hydrogen atom in the structural unit represented by formula(a2-2-1), the structural unit represented formula (a2-2-3), thestructural unit represented by formula (a2-2-6) and the structural unitrepresented by formula (a2-2-1), the structural unit represented byformula (a2-2-3) or the structural unit represented by formula (a2-2-6).

When the structural unit (a2-A) is included in the resin (A), thecontent of the structural unit (a2-A) is preferably 5 to 80 mol %, morepreferably 10 to 70 mol %, still more preferably 15 to 65 mol %, and yetmore preferably 20 to 65 mol %, based on all structural units.

The structural unit (a2-A) can be included in a resin (A) by treating aresin including a structural unit (a1-4) with an acid such asp-toluenesulfonic acid. The structural unit (a2-A) can also be includedin the resin (A) by polymerizing with acetoxystyrene and treating withan alkali such as tetramethylammonium hydroxide.

Examples of the structural unit having an alcoholic hydroxy group in thestructural unit (a2) include a structural unit represented by formula(a2-1) (hereinafter sometimes referred to as “structural unit (a2-1)”).

In formula (a2-1),

L^(a3) represents —O— or *—O—(CH₂)_(k2)—CO—O—,

k2 represents an integer of 1 to 7, and * represents a bonding site to—CO—,

R^(a14) represents a hydrogen atom or a methyl group,

R^(a15) and R^(a16) each independently represent a hydrogen atom, amethyl group or a hydroxy group, and

o1 represents an integer of 0 to 10.

In formula (a2-1), L^(a3) is preferably —O— or —O—(CH₂)_(f1)—CO—O— (f1represents an integer of 1 to 4), and more preferably —O—,

R^(a14) is preferably a methyl group,

R^(a15) is preferably a hydrogen atom,

R^(a16) is preferably a hydrogen atom or a hydroxy group, and

o1 is preferably an integer of 0 to 3, and more preferably 0 or 1.

The structural unit (a2-1) includes, for example, structural unitsderived from the monomers mentioned in JP 2010-204646 A. A structuralunit represented by any one of formula (a2-1-1) to formula (a2-1-6) ispreferable, a structural unit represented by any one of formula (a2-1-1)to formula (a2-1-4) is more preferable, and a structural unitrepresented by formula (a2-1-1) or formula (a2-1-3) is still morepreferable.

When the resin (A) includes the structural unit (a2-1), the content isusually 1 to 45 mol %, preferably 1 to 40 mol %, more preferably 1 to 35mol %, still more preferably 2 to 20 mol %, and yet more preferably 2 to10 mol %, based on all structural units of the resin (A).

<Structural Unit (a3)>

The lactone ring possessed by the structural unit (a3) may be amonocyclic ring such as a β-propiolactone ring, a γ-butyrolactone ringor a δ-valerolactone ring, or a condensed ring of a monocyclic lactonering and the other ring. Preferably, a γ-butyrolactone ring, anadamantanelactone ring or a bridged ring including a γ-butyrolactonering structure (e.g. a structural unit represented by the followingformula (a3-2)) is exemplified.

The structural unit (a3) is preferably a structural unit represented byformula (a3-1), formula (a3-2), formula (a3-3) or formula (a3-4). Thesestructural units may be included alone, or two or more structural unitsmay be included:

wherein, in formula (a3-1), formula (a3-2), formula (a3-3) and formula(a3-4),

L^(a4), L^(a5) and L^(a6) each independently represent —O— or a grouprepresented by *—O—(CH₂)_(k3)—CO—O— (k3 represents an integer of 1 to7),

L^(a7) represents —O—, *—O-L^(a8)-O—, *—O-L^(a8)-CO—O—,*—O-L^(a8)-CO—O-L^(a9)-CO—O— or *—O-L^(a8)-O—CO-L^(a9)-O—,

L^(a8) and L^(a9) each independently represent an alkanediyl grouphaving 1 to 6 carbon atoms,

* represents a bonding site to a carbonyl group,

R^(a18), R^(a19) and R^(a20) each independently represent a hydrogenatom or a methyl group,

R^(a24) represents an alkyl group having 1 to 6 carbon atoms which mayhave a halogen atom, a hydrogen atom or a halogen atom,

X^(a3) represents —CH₂— or an oxygen atom,

R^(a21) represents an aliphatic hydrocarbon group having 1 to 4 carbonatoms,

R^(a22), R^(a23) and R^(a25) each independently represent a carboxygroup, a cyano group or an aliphatic hydrocarbon group having 1 to 4carbon atoms,

p1 represents an integer of 0 to 5,

q1 represents an integer of 0 to 3,

r1 represents an integer of 0 to 3,

w1 represents an integer of 0 to 8, and

when p1, q1, r1 and/or w1 is/are 2 or more, a plurality of R^(a21),R^(a22), R^(a23) and/or R^(a25) may be the same or different from eachother.

Examples of the aliphatic hydrocarbon group in R^(a21), R^(a22), R^(a23)and R^(a25) include alkyl groups such as a methyl group, an ethyl group,a propyl group, an isopropyl group, a butyl group, a sec-butyl group anda tert-butyl group.

Examples of the halogen atom in R^(a24) include a fluorine atom, achlorine atom, a bromine atom and an iodine atom.

Examples of the alkyl group in R^(a24) include a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, a sec-butylgroup, a tert-butyl group, a pentyl group and a hexyl group, and thealkyl group is preferably an alkyl group having 1 to 4 carbon atoms, andmore preferably a methyl group or an ethyl group.

Examples of the alkyl group having a halogen atom in R^(a24) include atrifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group,a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butylgroup, a perfluorotert-butyl group, a perfluoropentyl group, aperfluorohexyl group, a trichloromethyl group, a tribromomethyl group, atriiodomethyl group and the like.

Examples of the alkanediyl group in L^(a8) and L^(a9) include amethylene group, an ethylene group, a propane-1,3-diyl group, apropane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diylgroup, a hexane-1,6-diyl group, a butane-1,3-diyl group, a2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, apentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group.

In formula (a3-1) to formula (a3-3), preferably, L^(a4) to L^(a6) areeach independently —O— or a group in which k3 is an integer of 1 to 4 in*—O—(CH₂)_(k3)—CO—O—, more preferably —O— and *—O—CH₂—CO—O—, and stillmore preferably an oxygen atom,

R^(a18) to R^(a21) are preferably a methyl group,

preferably, R^(a22) and R^(a23) are each independently a carboxy group,a cyano group or a methyl group, and

preferably, p1, q1 and r1 are each independently an integer of 0 to 2,and more preferably 0 or 1.

In formula (a3-4), R^(a24) is preferably a hydrogen atom or an alkylgroup having 1 to 4 carbon atoms, more preferably a hydrogen atom, amethyl group or an ethyl group, and still more preferably a hydrogenatom or a methyl group,

R^(a25) is preferably a carboxy group, a cyano group or a methyl group,

L^(a7) is preferably —O— or *—O-L^(a8)-CO—O—, and more preferably —O—,—O—CH₂—CO—O— or —O—C₂H₄—CO—O—, and

w1 is preferably an integer of 0 to 2, and more preferably 0 or 1.

Particularly, formula (a3-4) is preferably formula (a3-4)′:

wherein R^(a24) and L^(a7) are the same as defined above.

Examples of the structural unit (a3) include structural units derivedfrom the monomers mentioned in JP 2010-204646 A, the monomers mentionedin JP 2000-122294 A and the monomers mentioned in JP 2012-41274 A. Thestructural unit (a3) is preferably a structural unit represented by anyone of formula (a3-1-1), formula (a3-1-2), formula (a3-2-1), formula(a3-2-2), formula (a3-3-1), formula (a3-3-2) and formula (a3-4-1) toformula (a3-4-12), and structural units in which methyl groupscorresponding to R^(a18), R^(a19), R^(a20) and R^(a24) in formula (a3-1)to formula (a3-4) are substituted with hydrogen atoms in the abovestructural units.

When the resin (A) includes the structural unit (a3), the total contentis usually 5 to 70 mol %, preferably 10 to 65 mol %, and more preferably10 to 60 mol %, based on all structural units of the resin (A).

Each content of the structural unit (a3-1), the structural unit (a3-2),the structural unit (a3-3) or the structural unit (a3-4) is preferably 5to 60 mol %, more preferably 5 to 50 mol %, and still more preferably 10to 50 mol %, based on all structural units of the resin (A).

<Structural Unit (a4)>

Examples of the structural unit (a4) include the following structuralunits:

wherein, in formula (a4),

R⁴¹ represents a hydrogen atom or a methyl group, and

R⁴² represents a saturated hydrocarbon group having 1 to 24 carbon atomswhich has a fluorine atom, and —CH₂— included in the saturatedhydrocarbon group may be replaced by —O— or —CO.

Examples of the saturated hydrocarbon group represented by R⁴² include achain saturated hydrocarbon group and a monocyclic or polycyclicalicyclic saturated hydrocarbon group, and groups formed by combiningthese groups.

Examples of the chain saturated hydrocarbon group include a methylgroup, an ethyl group, a propyl group, a butyl group, a pentyl group, ahexyl group, a heptyl group, an octyl group, a decyl group, a dodecylgroup, a pentadecyl group, a hexadecyl group, a heptadecyl group and anoctadecyl group.

Examples of the monocyclic or polycyclic alicyclic saturated hydrocarbongroup include cycloalkyl groups such as a cyclopentyl group, acyclohexyl group, a cycloheptyl group and a cyclooctyl group; andpolycyclic alicyclic saturated hydrocarbon groups such as adecahydronaphthyl group, an adamantyl group, a norbornyl group and thefollowing groups (* represents a bonding site).

Examples of the group formed by combination include groups formed bycombining one or more alkyl groups or one or more alkanediyl groups withone or more alicyclic saturated hydrocarbon groups, and include analkanediyl group-alicyclic saturated hydrocarbon group, an alicyclicsaturated hydrocarbon group-alkyl group, an alkanediyl group-alicyclicsaturated hydrocarbon group-alkyl group and the like.

Examples of the structural unit (a4) include a structural unitrepresented by formula (a4-0), a structural unit represented by formula(a4-1) and a structural unit represented by formula (a4-4):

wherein, in formula (a4-0),

R⁵⁴ represents a hydrogen atom or a methyl group,

L^(4a) represents a single bond or an alkanediyl group having 1 to 4carbon atoms,

L^(3a) represents a perfluoroalkanediyl group having 1 to 8 carbon atomsor a perfluorocycloalkanediyl group having 3 to 12 carbon atoms, and

R⁶⁴ represents a hydrogen atom or a fluorine atom.

Examples of the alkanediyl group in L^(4a) include linear alkanediylgroups such as a methylene group, an ethylene group, a propane-1,3-diylgroup and a butane-1,4-diyl group; and branched alkanediyl groups suchas an ethane-1,1-diyl group, a propane-1,2-diyl group, a butane-1,3-diylgroup, a 2-methylpropane-1,3-diyl group and a 2-methylpropane-1,2-diylgroup.

Examples of the perfluoroalkanediyl group in L^(3a) include adifluoromethylene group, a perfluoroethylene group, aperfluoropropane-1,3-diyl group, a perfluoropropane-1,2-diyl group, aperfluoropropane-2,2-diyl group, a perfluorobutane-1,4-diyl group, aperfluorobutane-2,2-diyl group, a perfluorobutane-1,2-diyl group, aperfluoropentane-1,5-diyl group, a perfluoropentane-2,2-diyl group, aperfluoropentane-3,3-diyl group, a perfluorohexane-1,6-diyl group, aperfluorohexane-2,2-diyl group, a perfluorohexane-3,3-diyl group, aperfluoroheptane-1,7-diyl group, a perfluoroheptane-2,2-diyl group, aperfluoroheptane-3,4-diyl group, a perfluoroheptane-4,4-diyl group, aperfluorooctane-1,8-diyl group, a perfluorooctane-2,2-diyl group, aperfluorooctane-3,3-diyl group, a perfluorooctane-4,4-diyl group and thelike.

Examples of the perfluorocycloalkanediyl group in L^(3a) include aperfluorocyclohexanediyl group, a perfluorocyclopentanediyl group, aperfluorocycloheptanediyl group, a perfluoroadamantanediyl group and thelike.

L^(4a) is preferably a single bond, a methylene group or an ethylenegroup, and more preferably a single bond or a methylene group.

L^(3a) is preferably a perfluoroalkanediyl group having 1 to 6 carbonatoms, and more preferably a perfluoroalkanediyl group having 1 to 3carbon atoms.

Examples of the structural unit (a4-0) include the following structuralunits, and structural units in which a methyl group corresponding to R⁵⁴in the structural unit (a4-0) in the following structural units issubstituted with a hydrogen atom:

wherein, in formula (a4-1),

R^(a41) represents a hydrogen atom or a methyl group,

R^(a42) represents a hydrocarbon group having 1 to 20 carbon atoms whichmay have a substituent, and —CH₂— included in the saturated hydrocarbongroup may be replaced by —O— or —CO—,

A^(a41) represents an alkanediyl group having 1 to 6 carbon atoms whichmay have a substituent or a group represented by formula (a-g1), inwhich at least one of A^(a41) and R^(a42) has, as a substituent, ahalogen atom (preferably a fluorine atom):

[in which, in formula (a-g1),

s represents 0 or 1,

A^(a42) and A^(a44) each independently represent a divalent saturatedhydrocarbon group having 1 to 5 carbon atoms which may have asubstituent,

A^(a43) represents a single bond or a divalent saturated hydrocarbongroup having 1 to 5 carbon atoms which may have a substituent,

X^(a41) and X^(a42) each independently represent —O—, —CO—, —CO—O— or—O—CO—, in which the total number of carbon atoms of A^(a42), A^(a43),A^(a44), X^(a41) and X^(a42) is 7 or less], and

* is a bonding site and * at the right side is a bonding site to—O—CO—R^(a42).

Examples of the saturated hydrocarbon group in R^(a42) include an alkylgroup, a monocyclic or a polycyclic alicyclic hydrocarbon group, andgroups formed by combining these groups.

Examples of the alkyl group include a methyl group, an ethyl group, apropyl group, a butyl group, a pentyl group, a hexyl group, a heptylgroup, an octyl group, a decyl group, a dodecyl group, a pentadecylgroup, a hexadecyl group, a heptadecyl group and an octadecyl group.

Examples of the monocyclic or polycyclic saturated alicyclic hydrocarbongroup include cycloalkyl groups such as a cyclopentyl group, acyclohexyl group, a cycloheptyl group and a cyclooctyl group; andpolycyclic alicyclic hydrocarbon groups such as a decahydronaphthylgroup, an adamantyl group, a norbornyl group and the following groups (*represents a bonding site).

Examples of the group formed by combination include groups formed bycombining one or more alkyl groups or one or more alkanediyl groups withone or more saturated alicyclic hydrocarbon groups, and include analkanediyl group-saturated alicyclic hydrocarbon group, a saturatedalicyclic hydrocarbon group-alkyl group, an alkanediyl group-saturatedalicyclic hydrocarbon group-alkyl group and the like.

Examples of the substituent possessed by R^(a42) include at least oneselected from the group consisting of a halogen atom and a grouprepresented by formula (a-g3). Examples of the halogen atom include afluorine atom, a chlorine atom, a bromine atom and an iodine atom, and afluorine atom is preferable:

*—X^(a43)-A^(a54)  (a-g3)

wherein, in formula (a-g3),

X^(a43) represents an oxygen atom, a carbonyl group, *—O—CO— or *—CO—O—(* represents a bonding site to R^(a42)),

A^(a45) represents a saturated hydrocarbon group having 1 to 17 carbonatoms which may have a halogen atom, and

* represents a bonding site.

In R^(a42)—X^(a43)-A^(a45), when R^(a42) has no halogen atom, A^(a45)represents a saturated hydrocarbon group having 1 to 17 carbon atomshaving at least one halogen atom.

Examples of the saturated hydrocarbon group in A^(a45) include alkylgroups such as a methyl group, an ethyl group, a propyl group, a butylgroup, a pentyl group, a hexyl group, a heptyl group, an octyl group, adecyl group, a dodecyl group, a pentadecyl group, a hexadecyl group, aheptadecyl group and an octadecyl group; monocyclic alicyclichydrocarbon groups such as a cyclopentyl group, a cyclohexyl group, acycloheptyl group and a cyclooctyl group; and polycyclic alicyclichydrocarbon groups such as a decahydronaphthyl group, an adamantylgroup, a norbornyl group and the following groups (* represents abonding site):

Examples of the group formed by combination include a group obtained bycombining one or more alkyl groups or one or more alkanediyl groups withone or more alicyclic hydrocarbon groups, and include an -alkanediylgroup-alicyclic hydrocarbon group, an -alicyclic hydrocarbon group-alkylgroup, an -alkanediyl group-alicyclic hydrocarbon group-alkyl group andthe like.

R^(d42) is preferably a saturated hydrocarbon group which may have ahalogen atom, and more preferably an alkyl group having a halogen atomand/or a saturated hydrocarbon group having a group represented byformula (a-g3).

When R^(d42) is a saturated hydrocarbon group having a halogen atom, asaturated hydrocarbon group having a fluorine atom is preferable, aperfluoroalkyl group or a perfluorocycloalkyl group is more preferable,a perfluoroalkyl group having 1 to 6 carbon atoms is still morepreferable, and a perfluoroalkyl group having 1 to 3 carbon atoms isparticularly preferable. Examples of the perfluoroalkyl group include aperfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group,a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group,a perfluoroheptyl group and a perfluorooctyl group. Examples of theperfluorocycloalkyl group include a perfluorocyclohexyl group and thelike.

When R^(a42) is a saturated hydrocarbon group having a group representedby formula (a-g3), the total number of carbon atoms of R^(d42) ispreferably 15 or less, and more preferably 12 or less, including thenumber of carbon atoms included in the group represented by formula(a-g3). When having the group represented by formula (a-g3) as thesubstituent, the number thereof is preferably 1.

When R^(a42) is a saturated hydrocarbon group having the grouprepresented by formula (a-g3), R^(a42) is still more preferably a grouprepresented by formula (a-g2):

*-A^(a46)-X^(a44)-A^(a47)  (a-g2)

wherein, in formula (a-g2),

A^(a46) represents a saturated hydrocarbon group having 1 to 17 carbonatoms which may have a halogen atom,

X^(a44) represents *—O—CO— or *—CO—O— (* represents a bonding site toA^(a46)),

A^(a47) represents a saturated hydrocarbon group having 1 to 17 carbonatoms which may have a halogen atom,

the total number of carbon atoms of A^(a46), A^(a47) and X^(a44) is 18or less, and at least one of A^(a46) and A^(a47) has at least onehalogen atom, and

* represents a bonding site to a carbonyl group.

The number of carbon atoms of the saturated hydrocarbon group of A^(a46)is preferably 1 to 6, and more preferably 1 to 3.

The number of carbon atoms of the saturated hydrocarbon group of A^(a47)is preferably 4 to 15, and more preferably 5 to 12, and A^(a47) is stillmore preferably a cyclohexyl group or an adamantyl group.

Preferred structure of the group represented by formula (a-g2) is thefollowing structure (* is a bonding site to a carbonyl group).

Examples of the alkanediyl group in A^(a41) include linear alkanediylgroups such as a methylene group, an ethylene group, a propane-1,3-diylgroup, a butane-1,4-diyl group, a pentane-1,5-diyl group and ahexane-1,6-diyl group; and branched alkanediyl groups such as apropane-1,2-diyl group, a butane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a 1-methylbutane-1,4-diyl group and a2-methylbutane-1,4-diyl group.

Examples of the substituent in the alkanediyl group represented byA^(a41) include a hydroxy group and an alkoxy group having 1 to 6 carbonatoms.

A^(a41) is preferably an alkanediyl group having 1 to 4 carbon atoms,more preferably an alkanediyl group having 2 to 4 carbon atoms, andstill more preferably an ethylene group.

Examples of the divalent saturated hydrocarbon group represented byA^(a42), A^(a43) and A^(a44) in the group represented by formula (a-g1)include a linear or branched divalent alkyl group and a monocyclicdivalent alicyclic saturated hydrocarbon group, and a divalent saturatedhydrocarbon group formed by combining an alkyl group and an alicyclicsaturated hydrocarbon group. Specific examples thereof include amethylene group, an ethylene group, a propane-1,3-diyl group, apropane-1,2-diyl group, a butane-1,4-diyl group, a1-methylpropane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group and the like.

Examples of the substituent of the divalent saturated hydrocarbon grouprepresented by A^(a42), A^(a43) and A^(a44) include a hydroxy group andan alkoxy group having 1 to 6 carbon atoms.

s is preferably 0.

In the group represented by formula (a-g1), examples of the group inwhich X^(a42) is —O—, —CO—, —CO—O— or —O—CO-include the followinggroups. In the following exemplification, * and ** each represent abonding site, and ** is a bonding site to —O—CO—R^(a42).

Examples of the structural unit represented by formula (a4-1) includethe following structural units, and structural units in which a methylgroup corresponding to A^(a41) in the structural unit represented byformula (a4-1) in the following structural units is substituted with ahydrogen atom.

Examples of the structural unit represented by formula (a4-1) include astructural unit represented by formula (a4-2) and a structural unitrepresented by formula (a4-3):

wherein, in formula (a4-2),

R^(f5) represents a hydrogen atom or a methyl group,

L⁴⁴ represents an alkanediyl group having 1 to 6 carbon atoms, and —CH₂—included in the alkanediyl group may be replaced by —O— or —CO—,

R^(f6) represents a saturated hydrocarbon group having 1 to 20 carbonatoms having a fluorine atom, and

the upper limit of the total number of carbon atoms of L⁴⁴ and R^(f6) is21.

Examples of the alkanediyl group having 1 to 6 carbon atoms of L⁴⁴include the same groups as mentioned for A^(a41).

Examples of the saturated hydrocarbon group of R^(f6) include the samegroups as mentioned for R⁴².

The alkanediyl group in L⁴⁴ is preferably an alkanediyl group having 2to 4 carbon atoms, and more preferably an ethylene group.

The structural unit represented by formula (a4-2) includes, for example,structural units represented by formula (a4-1-1) to formula (a4-1-11). Astructural unit in which a methyl group corresponding to R^(f5) in thestructural unit (a4-2) is substituted with a hydrogen atom is alsoexemplified as the structural unit represented by formula (a4-2):

wherein, in formula (a4-3),

R^(f) represents a hydrogen atom or a methyl group,

L⁵ represents an alkanediyl group having 1 to 6 carbon atoms,

A^(f13) represents a divalent saturated hydrocarbon group having 1 to 18carbon atoms which may have a fluorine atom,

X^(f12) represents *—O—CO— or *—CO—O— (* represents a bonding site toA^(f13)),

A^(f14) represents a saturated hydrocarbon group having 1 to 17 carbonatoms which may have a fluorine atom, and

at least one of A^(f13) and A^(f14) has a fluorine atom, and the upperlimit of the total number of carbon atoms of L⁵, A^(f13) and A^(f14) is20.

Examples of the alkanediyl group in L⁵ include those which are the sameas mentioned in the alkanediyl group of A^(a41).

The divalent saturated hydrocarbon group which may have a fluorine atomin A^(f13) is preferably a divalent chain saturated hydrocarbon groupwhich may have a fluorine atom and a divalent alicyclic saturatedhydrocarbon group which may have a fluorine atom, and more preferably aperfluoroalkanediyl group.

Examples of the divalent chain saturated hydrocarbon group which mayhave a fluorine atom include alkanediyl groups such as a methylenegroup, an ethylene group, a propanediyl group, a butanediyl group and apentanediyl group; and perfluoroalkanediyl groups such as adifluoromethylene group, a perfluoroethylene group, aperfluoropropanediyl group, a perfluorobutanediyl group and aperfluoropentanediyl group.

The divalent alicyclic saturated hydrocarbon group which may have afluorine atom may be either monocyclic or polycyclic. Examples of themonocyclic group include a cyclohexanediyl group and aperfluorocyclohexanediyl group. Examples of the polycyclic group includean adamantanediyl group, a norbornanediyl group, aperfluoroadamantanediyl group and the like.

Examples of the saturated hydrocarbon group and the saturatedhydrocarbon group which may have a fluorine atom for A^(f14) include thesame groups as mentioned for R^(a42). Of these groups, preferable arefluorinated alkyl groups such as a trifluoromethyl group, adifluoromethyl group, a methyl group, a perfluoroethyl group, a2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethylgroup, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, apropyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutylgroup, a butyl group, a perfluoropentyl group, a2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl group,a perfluorohexyl group, a heptyl group, a perfluoroheptyl group, anoctyl group and a perfluorooctyl group; a cyclopropylmethyl group, acyclopropyl group, a cyclobutylmethyl group, a cyclopentyl group, acyclohexyl group, a perfluorocyclohexyl group, an adamantyl group, anadamantylmethyl group, an adamantyldimethyl group, a norbornyl group, anorbornylmethyl group, a perfluoroadamantyl group, aperfluoroadamantylmethyl group and the like.

In formula (a4-3), L⁵ is preferably an ethylene group.

The divalent saturated hydrocarbon group of A^(f13) is preferably agroup including a chain saturated hydrocarbon group having 1 to 6 carbonatoms and an alicyclic saturated hydrocarbon group having 3 to 12 carbonatoms, and more preferably a chain saturated hydrocarbon group having 2to 3 carbon atoms.

The saturated hydrocarbon group of A^(f14) is preferably a groupincluding a chain saturated hydrocarbon group having 3 to 12 carbonatoms and an alicyclic saturated hydrocarbon group having 3 to 12 carbonatoms, and more preferably a group including a chain saturatedhydrocarbon group having 3 to 10 carbon atoms and an alicyclic saturatedhydrocarbon group having 3 to 10 carbon atoms. Of these groups, A^(f14)is preferably a group including an alicyclic saturated hydrocarbon grouphaving 3 to 12 carbon atoms, and more preferably a cyclopropylmethylgroup, a cyclopentyl group, a cyclohexyl group, a norbornyl group and anadamantyl group.

The structural unit represented by formula (a4-3) includes, for example,structural units represented by formula (a4-1′-1) to formula (a4-1′-11).A structural unit in which a methyl group corresponding to R^(f7) in thestructural unit (a4-3) is substitute with a hydrogen atom is alsoexemplified as the structural unit represented by formula (a4-3).

It is also possible to exemplify, as the structural unit (a4), astructural unit represented by formula (a4-4):

wherein, in formula (a4-4),

R^(f21) represents a hydrogen atom or a methyl group,

A^(f21) represents —(CH₂)_(j1)—, —(CH₂)_(j2)—O—(CH₂)_(j3)— or—(CH₂)_(j4)—CO—O—(CH₂)_(j5)—,

j1 to j5 each independently represent an integer of 1 to 6, and

R^(f22) represents a saturated hydrocarbon group having 1 to 10 carbonatoms having a fluorine atom.

Examples of the saturated hydrocarbon group of R^(f22) of formula (a4-1)include those which are the same as the saturated hydrocarbon grouprepresented by R^(a42). R^(f22) is preferably an alkyl group having 1 to10 carbon atoms having a fluorine atom or an alicyclic saturatedhydrocarbon group having 1 to 10 carbon atoms having a fluorine atom,more preferably an alkyl group having 1 to 10 carbon atoms having afluorine atom, and still more preferably, an alkyl group having 1 to 6carbon atoms having a fluorine atom.

In formula (a4-4), A^(f21) is preferably —(CH₂)_(j1)—, more preferablyan ethylene group or a methylene group, and still more preferably amethylene group.

The structural unit represented by formula (a4-4) includes, for example,the following structural units and structural units in which a methylgroup corresponding to R^(f21) in the structural unit (a4-4) issubstituted with a hydrogen atom in structural units represented by thefollowing formulas.

When the resin (A) includes the structural unit (a4), the content ispreferably 1 to 20 mol %, more preferably 2 to 15 mol %, and still morepreferably 3 to 10 mol %, based on all structural units of the resin(A).

<Structural Unit (a5)>

Examples of a non-leaving hydrocarbon group possessed by the structuralunit (a5) include groups having a linear, branched or cyclic hydrocarbongroup. Of these, the structural unit (a5) is preferably a group havingan alicyclic hydrocarbon group.

The structural unit (a5) includes, for example, a structural unitrepresented by formula (a5-1):

wherein, in formula (a5-1),

R⁵¹ represents a hydrogen atom or a methyl group,

R⁵² represents an alicyclic hydrocarbon group having 3 to 18 carbonatoms, and a hydrogen atom included in the alicyclic hydrocarbon groupmay be substituted with an aliphatic hydrocarbon group having 1 to 8carbon atoms, and

L⁵⁵ represents a single bond or a divalent saturated hydrocarbon grouphaving 1 to 18 carbon atoms, and —CH₂-included in the saturatedhydrocarbon group may be replaced by —O— or —CO—.

The alicyclic hydrocarbon group in R⁵² may be either monocyclic orpolycyclic. The monocyclic alicyclic hydrocarbon group includes, forexample, a cyclopropyl group, a cyclobutyl group, a cyclopentyl groupand a cyclohexyl group. The polycyclic alicyclic hydrocarbon groupincludes, for example, an adamantyl group and a norbornyl group.

The aliphatic hydrocarbon group having 1 to 8 carbon atoms includes, forexample, alkyl groups such as a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, a sec-butyl group, atert-butyl group, a pentyl group, a hexyl group, an octyl group and a2-ethylhexyl group.

Examples of the alicyclic hydrocarbon group having a substituentincludes a 3-hydroxyadamantyl group, a 3-methyladamantyl group and thelike.

R⁵² is preferably an unsubstituted alicyclic hydrocarbon group having 3to 18 carbon atoms, and more preferably an adamantyl group, a norbornylgroup or a cyclohexyl group.

Examples of the divalent saturated hydrocarbon group in L⁵⁵ include adivalent chain saturated hydrocarbon group and a divalent alicyclicsaturated hydrocarbon group, and a divalent chain saturated hydrocarbongroup is preferable.

The divalent chain saturated hydrocarbon group includes, for example,alkanediyl groups such as a methylene group, an ethylene group, apropanediyl group, a butanediyl group and a pentanediyl group.

The divalent alicyclic saturated hydrocarbon group may be eithermonocyclic or polycyclic. Examples of the monocyclic alicyclic saturatedhydrocarbon group include cycloalkanediyl groups such as acyclopentanediyl group and a cyclohexanediyl group. Examples of thepolycyclic divalent alicyclic saturated hydrocarbon group include anadamantanediyl group and a norbornanediyl group.

The group in which —CH₂— included in the divalent saturated hydrocarbongroup represented by L⁵⁵ is replaced by —O— or —CO— includes, forexample, groups represented by formula (L1-1) to formula (L1-4). In thefollowing formulas, * and ** each represent a bonding site, and *represents a bonding site to an oxygen atom.

In formula (L1-1),

X^(x1) represents *—O—CO— or *—CO—O— (* represents a bonding site toL^(x1)),

L^(x1) represents a divalent aliphatic saturated hydrocarbon grouphaving 1 to 16 carbon atoms,

L^(x2) represents a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 15 carbon atoms, and the total number ofcarbon atoms of L^(x1) and L^(x2) is 16 or less.

In formula (L1-2),

L^(x3) represents a divalent aliphatic saturated hydrocarbon grouphaving 1 to 17 carbon atoms,

L^(x4) represents a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 16 carbon atoms, and the total number ofcarbon atoms of L^(x3) and L^(x4) is 17 or less.

In formula (L1-3),

L^(x5) represents a divalent aliphatic saturated hydrocarbon grouphaving 1 to 15 carbon atoms,

L^(x6) and L^(x7) each independently represent a single bond or adivalent aliphatic saturated hydrocarbon group having 1 to 14 carbonatoms, and

the total number of carbon atoms of L^(x5), L^(x6) and L^(x7) is 15 orless.

In formula (L1-4),

L^(x8) and L^(x) represents a single bond or a divalent aliphaticsaturated hydrocarbon group having 1 to 12 carbon atoms,

W^(x1) represents a divalent alicyclic saturated hydrocarbon grouphaving 3 to 15 carbon atoms, and the total number of carbon atoms ofL^(x8), L^(x9) and W^(x1) is 15 or less.

L^(x1) is preferably a divalent aliphatic saturated hydrocarbon grouphaving 1 to 8 carbon atoms, and more preferably a methylene group or anethylene group.

L^(x2) is preferably a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 8 carbon atoms, and more preferably asingle bond.

L^(x3) is preferably a divalent aliphatic saturated hydrocarbon grouphaving 1 to 8 carbon atoms.

L^(x4) is preferably a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 8 carbon atoms.

L^(x)S is preferably a divalent aliphatic saturated hydrocarbon grouphaving 1 to 8 carbon atoms, and more preferably a methylene group or anethylene group.

L^(x6) is preferably a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 8 carbon atoms, and more preferably amethylene group or an ethylene group.

L^(x7) is preferably a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 8 carbon atoms.

L^(x8) is preferably a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 8 carbon atoms, and more preferably asingle bond or a methylene group.

L^(x9) is preferably a single bond or a divalent aliphatic saturatedhydrocarbon group having 1 to 8 carbon atoms, and more preferably asingle bond or a methylene group.

W^(x1) is preferably a divalent alicyclic saturated hydrocarbon grouphaving 3 to 10 carbon atoms, and more preferably a cyclohexanediyl groupor an adamantanediyl group.

The group represented by formula (L1-1) includes, for example, thefollowing divalent groups.

The group represented by formula (L1-2) includes, for example, thefollowing divalent groups.

The group represented by formula (L1-3) includes, for example, thefollowing divalent groups.

The group represented by formula (L1-4) includes, for example, thefollowing divalent groups.

L⁵⁵ is preferably a single bond or a group represented by formula(L1-1).

Examples of the structural unit (a5-1) include the following structuralunits and structural units in which a methyl group corresponding to R⁵¹in the structural unit (a5-1) in the following structural units issubstituted with a hydrogen atom.

When the resin (A) includes the structural unit (a5), the content ispreferably 1 to 30 mol %, more preferably 2 to 20 mol %, and still morepreferably 3 to 15 mol %, based on all structural units of the resin(A).

<Structural Unit (II)>

The resin (A) may further include a structural unit which is decomposedupon exposure to radiation to generate an acid (hereinafter sometimesreferred to as “structural unit (II)). Specific examples of thestructural unit (II) include the structural units mentioned in JP2016-79235 A, and a structural unit having a sulfonate group or acarboxylate group and an organic cation in a side chain or a structuralunit having a sulfonio group and an organic anion in a side chain arepreferable.

The structural unit having a sulfonate group or a carboxylate group andan organic cation in a side chain is preferably a structural unitrepresented by formula (II-2-A′):

wherein, in formula (II-2-A′),

X^(III3) represents a divalent saturated hydrocarbon group having 1 to18 carbon atoms, —CH₂— included in the saturated hydrocarbon group maybe replaced by —O—, —S— or —CO—, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a halogen atom, analkyl group having 1 to 6 carbon atoms which may have a halogen atom, ora hydroxy group,

A^(x1) represents an alkanediyl group having 1 to 8 carbon atoms, and ahydrogen atom included in the alkanediyl group may be substituted with afluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms,

RA⁻ represents a sulfonate group or a carboxylate group,

R^(III3) represents a hydrogen atom, a halogen atom or an alkyl grouphaving 1 to 6 carbon atoms which may have a halogen atom, and

ZA⁺ represents an organic cation.

Examples of the halogen atom represented by R^(III3) include a fluorineatom, a chlorine atom, a bromine atom and an iodine atom.

Examples of the alkyl group having 1 to 6 carbon atoms which may have ahalogen atom represented by R^(III3) include those which are the same asthe alkyl group having 1 to 6 carbon atoms which may have a halogen atomrepresented by R^(a8).

Examples of the alkanediyl group having 1 to 8 carbon atoms representedby A^(x1) include a methylene group, an ethylene group, apropane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diylgroup, a hexane-1,6-diyl group, an ethane-1,1-diyl group, apropane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diylgroup, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, a2-methylbutane-1,4-diyl group and the like.

Examples of the perfluoroalkyl group having 1 to 6 carbon atoms in whicha hydrogen atom may be substituted in A^(x1) include a trifluoromethylgroup, a perfluoroethyl group, a perfluoropropyl group, aperfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butylgroup, a perfluorotert-butyl group, a perfluoropentyl group, aperfluorohexyl group and the like.

Examples of the divalent saturated hydrocarbon group having 1 to 18carbon atoms represented by X^(III3) include a linear or branchedalkanediyl group, a monocyclic or a polycyclic divalent alicyclicsaturated hydrocarbon group, or a combination thereof.

Specific examples thereof include linear alkanediyl groups such as amethylene group, an ethylene group, a propane-1,3-diyl group, apropane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diylgroup, a hexane-1,6-diyl group, a heptane-1,7-diyl group, anoctane-1,8-diyl group, a nonane-1,9-diyl group, a decane-1,10-diylgroup, an undecane-1,11-diyl group and a dodecane-1,12-diyl group;branched alkanediyl groups such as a butane-1,3-diyl group, a2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, apentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group; divalentmonocyclic alicyclic saturated hydrocarbon groups such as acyclobutane-1,3-diyl group, a cyclopentane-1,3-diyl group, acyclohexane-1,4-diyl group and a cyclooctane-1,5-diyl group; anddivalent polycyclic alicyclic saturated hydrocarbon groups such as anorbornane-1,4-diyl group, a norbornane-2,5-diyl group, anadamantane-1,5-diyl group and an adamantane-2,6-diyl group.

Those in which —CH₂— included in the saturated hydrocarbon group arereplaced by —O—, —S— or —CO— include, for example, divalent groupsrepresented by formula (X1) to formula (X53). Before replacing —CH₂—included in the saturated hydrocarbon group by —O—, —S— or —CO—, thenumber of carbon atoms is 17 or less. In the following formulas, * and** represent a bonding site, and * represents a bonding site to A^(x1).

X³ represents a divalent saturated hydrocarbon group having 1 to 16carbon atoms.

X⁴ represents a divalent saturated hydrocarbon group having 1 to 15carbon atoms.

X⁵ represents a divalent saturated hydrocarbon group having 1 to 13carbon atoms.

X⁶ represents a divalent saturated hydrocarbon group having 1 to 14carbon atoms.

X⁷ represents a trivalent saturated hydrocarbon group having 1 to 14carbon atoms.

X⁸ represents a divalent saturated hydrocarbon group having 1 to 13carbon atoms.

Examples of the organic cation represented by ZA⁺ include those whichare the same as the cation Z1⁺ in the acid generator (B1).

The structural unit represented by formula (II-2-A′) is preferably astructural unit represented by formula (II-2-A):

wherein, in formula (II-2-A), R^(III3), X^(III3) and ZA⁺ are the same asdefined above,

z represents an integer of 0 to 6,

R^(III2) and R^(III4) each independently represent a hydrogen atom, afluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, andwhen z is 2 or more, a plurality of R^(III2) and R^(III4) may be thesame or different from each other, and

Q^(a) and Q^(b) each independently represent a fluorine atom or aperfluoroalkyl group having 1 to 6 carbon atoms.

Examples of the perfluoroalkyl group having 1 to 6 carbon atomsrepresented by R^(III2), R^(III4), Q^(a) and Q^(b) include those whichare the same as the perfluoroalkyl group having 1 to 6 carbon atomsrepresented by Q^(b1).

The structural unit represented by formula (II-2-A) is preferably astructural unit represented by formula (II-2-A-1):

wherein, in formula (II-2-A-1),

R^(III2), R^(III3), R^(III4), Q^(a), Q^(b), z and ZA⁺ are the same asdefined above,

R^(III5) represents a saturated hydrocarbon group having 1 to 12 carbonatoms, and

X^(I2) represents a divalent saturated hydrocarbon group having 1 to 11carbon atoms, —CH₂— included in the saturated hydrocarbon group may bereplaced by —O—, —S— or —CO—, and a hydrogen atom included in thesaturated hydrocarbon group may be substituted with a halogen atom or ahydroxy group.

Examples of the saturated hydrocarbon group having 1 to 12 carbon atomsrepresented by R^(III5) include linear or branched alkyl groups such asa methyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, ahexyl group, a heptyl group, an octyl group, a nonyl group, a decylgroup, an undecyl group and a dodecyl group.

Examples of the divalent saturated hydrocarbon group represented byX^(I2) include those which are the same as the divalent saturatedhydrocarbon group represented by X^(III3).

The structural unit represented by formula (II-2-A-1) is preferably astructural unit represented by formula (II-2-A-2):

wherein, in formula (II-2-A-2), R^(III3), R^(III5) and ZA⁺ are the sameas defined above, and

m and n each independently represent 1 or 2.

The structural unit represented by formula (II-2-A′) includes, forexample, the following structural units and the structural unitsmentioned in WO 2012/050015 A. ZA⁺ represents an organic cation.

The structural unit having a sulfonio group and an organic anion in aside chain is preferably a structural unit represented by formula(II-1-1):

wherein, in formula (II-1-1),

A^(II1) represents a single bond or a divalent linking group,

R^(II1) represents a divalent aromatic hydrocarbon group having 6 to 18carbon atoms,

R^(II2) and R^(II3) each independently represent a hydrocarbon grouphaving 1 to 18 carbon atoms, and R^(II2) and R^(II3) may be bonded toeach other to form a ring together with sulfur atoms to which R^(II2)and R^(II3) are bonded,

R^(II4) represents a hydrogen atom, a halogen atom or an alkyl grouphaving 1 to 6 carbon atoms which may have a halogen atom, and

A⁻ represents an organic anion.

Examples of the divalent aromatic hydrocarbon group having 6 to 18carbon atoms represented by R^(II1) include a phenylene group and anaphthylene group.

Examples of the hydrocarbon group represented by R^(II2) and R^(II3)include an alkyl group, an alicyclic hydrocarbon group, an aromatichydrocarbon group, and groups formed by combining these groups.

Examples of the alkyl group and the alicyclic hydrocarbon group includethose which are the same as mentioned above.

Examples of the aromatic hydrocarbon group include aryl groups such as aphenyl group, a naphthyl group, an anthryl group, a biphenyl group and aphenanthryl group.

Examples of the combined group include groups obtained by combining theabove-mentioned alkyl groups and alicyclic hydrocarbon groups, aralkylgroups such as a benzyl group, aromatic hydrocarbon groups having analkyl group (a p-methylphenyl group, a p-tert-butylphenyl group, a tolylgroup, a xylyl group, a cumenyl group, a mesityl group, a2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), aromatichydrocarbon groups having an alicyclic hydrocarbon group (ap-cyclohexylphenyl group, a p-adamantylphenyl group, etc.),aryl-cycloalkyl groups such as a phenylcyclohexyl group and the like.

Examples of the halogen atom represented by R^(II4) include a fluorineatom, a chlorine atom, a bromine atom and an iodine atom.

Examples of the alkyl group having 1 to 6 carbon atoms which may have ahalogen atom represented by R^(II4) include those which are the same asthe alkyl group having 1 to 6 carbon atoms which may have a halogen atomrepresented by R^(a8).

Examples of the divalent linking group represented by A^(II1) include adivalent saturated hydrocarbon group having 1 to 18 carbon atoms, and—CH₂— included in the divalent saturated hydrocarbon group may bereplaced by —O—, —S— or —CO—. Specific examples thereof include thosewhich are the same as the divalent saturated hydrocarbon group having 1to 18 carbon atoms represented by X^(III3).

Examples of the structural unit including a cation in formula (II-1-1)include the following structural units.

Examples of the organic anion represented by A-include a sulfonic acidanion, a sulfonylimide anion, a sulfonylmethide anion and a carboxylicacid anion. The organic anion represented by A⁻ is preferably a sulfonicacid anion, and examples of the sulfonic acid anion include those whichare the same as the anion included in the above-mentioned saltrepresented by formula (B1).

Examples of the sulfonylimide anion represented by A-include thefollowings.

Examples of the sulfonylmethide anion include the followings.

Examples of the carboxylic acid anion include the followings.

Examples of the structural unit represented by formula (II-1-1) includestructural units represented by the following formulas.

When the structural unit (ii) is included in the resin (A), the contentof the structural unit (II) is preferably 1 to 20 mol %, more preferably2 to 15 mol %, and still more preferably 3 to 10 mol %, based on allstructural units of the resin (A).

The resin (A) may include structural units other than the structuralunits mentioned above, and examples of such structural unit includestructural units well-known in the art.

The resin (A) is preferably a resin composed of a structural unit (a1)and a structural unit (s), i.e., a copolymer of a monomer (a1) and amonomer (s).

The structural unit (a1) is preferably at least one selected from thegroup consisting of a structural unit (a1-0), a structural unit (a1-1)and a structural unit (a1-2) (preferably the structural unit having acyclohexyl group, and a cyclopentyl group), more preferably at leasttwo, and still more preferably at least two selected from the groupconsisting of a structural unit (a1-1) and a structural unit (a1-2).

The structural unit (s) is preferably at least one selected from thegroup consisting of a structural unit (a2) and a structural unit (a3).The structural unit (a2) is preferably a structural unit (a2-1) or astructural unit (a2-A). The structural unit (a3) is preferably at leastone selected from the group consisting of a structural unit representedby formula (a3-1), a structural unit represented by formula (a3-2) and astructural unit represented by formula (a3-4).

The respective structural units constituting the resin (A) may be usedalone, or two or more structural units may be used in combination. Usinga monomer from which these structural units are derived, it is possibleto produce by a known polymerization method (e.g. radical polymerizationmethod). The content of the respective structural units included in theresin (A) can be adjusted according to the amount of the monomer used inthe polymerization.

The weight-average molecular weight of the resin (A) is preferably 2,000or more (more preferably 2,500 or more, and still more preferably 3,000or more), and 50,000 or less (more preferably 30,000 or less, and stillmore preferably 15,000 or less). In the present specification, theweight-average molecular weight is a value determined by gel permeationchromatography under the conditions mentioned in Examples.

<Resin Other than Resin (A)>

The resist composition of the present invention preferably furtherincludes a resin other than the resin (A).

The resin other than the resin (A) includes, for example, a resinincluding a structural unit (a4) or a structural unit (a5) (hereinaftersometimes referred to as resin (X)).

The resin (X) is preferably a resin including a structural unit (a4),particularly.

In the resin (X), the content of the structural unit (a4) is preferably30 mol % or more, more preferably 40 mol % or more, and still morepreferably 45 mol % or more, based on the total of all structural unitsof the resin (X).

Examples of the structural unit, which may be further included in theresin (X), include a structural unit (a2), a structural unit (a3) andstructural units derived from other known monomers. Particularly, theresin (X) is preferably a resin composed only of a structural unit (a4)and/or a structural unit (a5), and more preferably a resin composed onlyof a structural unit (a4).

The respective structural unit constituting the resin (X) may be usedalone, or two or more structural units may be used in combination. Usinga monomer from which these structural units are derived, it is possibleto produce by a known polymerization method (e.g. radical polymerizationmethod). The content of the respective structural units included in theresin (X) can be adjusted according to the amount of the monomer used inthe polymerization.

The weight-average molecular weight of the resin (X) is preferably 6,000or more (more preferably 7,000 or more) and 80,000 or less (morepreferably 60,000 or less). The measurement means of the weight-averagemolecular weight of the resin (X) is the same as in the case of theresin (A).

When the resist composition includes the resin (X), the content ispreferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass,still more preferably 1 to 40 parts by mass, particularly preferably 1to 30 parts by mass, and particularly preferably 1 to 8 parts by mass,based on 100 parts by mass of the resin (A).

The content of the resin (A) in the resist composition is preferably 80%by mass or more and 99% by mass or less, and more preferably 90% by massor more and 99% by mass or less, based on the solid component of theresist composition. When including resins other than the resin (A), thetotal content of the resin (A) and resins other than the resin (A) ispreferably 80% by mass or more and 99′ by mass or less, and morepreferably 90% by mass or more and 99% by mass or less, based on thesolid component of the resist composition. In the present specification,“solid component of the resist composition” means the total amount ofcomponents obtained by removing a solvent (E) mentioned later from thetotal amount of the resist composition. The solid component of theresist composition and the content of the resin thereto can be measuredby a known analysis means such as liquid chromatography or gaschromatography.

<Solvent (E)>

The content of the solvent (E) in the resist composition is usually 90%by mass or more and 99.9% by mass or less, preferably 92% by mass ormore and 99% by mass or less, and more preferably 94% by mass or moreand 99% by mass or less. The content of the solvent (E) can be measured,for example, by a known analysis means such as liquid chromatography orgas chromatography.

Examples of the solvent (E) include glycol ether esters such asethylcellosolve acetate, methylcellosolve acetate and propylene glycolmonomethyl ether acetate; glycol ethers such as propylene glycolmonomethyl ether; esters such as ethyl lactate, butyl acetate, amylacetate and ethyl pyruvate; ketones such as acetone, methyl isobutylketone, 2-heptanone and cyclohexanone; and cyclic esters such asγ-butyrolactone. The solvent (E) may be used alone, or two or moresolvents may be used.

<Quencher (C)>

Examples of the quencher (C) include a basic nitrogen-containing organiccompound, and a salt generating an acid having an acidity lower thanthat of an acid generated from an acid generator (B). The content of thequencher (C) is preferably about 0.01 to 5% by mass based on the amountof the solid component of the resist composition.

Examples of the basic nitrogen-containing organic compound include amineand an ammonium salt. Examples of the amine include an aliphatic amineand an aromatic amine. Examples of the aliphatic amine include a primaryamine, a secondary amine and a tertiary amine.

Examples of the amine include 1-naphthylamine, 2-naphthylamine, aniline,diisopropylaniline, 2-, 3- or 4-methylaniline, 4-nitroaniline,N-methylaniline, N,N-dimethylaniline, diphenylamine, hexylamine,heptylamine, octylamine, nonylamine, decylamine, dibutylamine,dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, triethylamine, trimethylamine, tripropylamine,tributylamine, tripentylamine, trihexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, methyldibutylamine,methyldipentylamine, methyldihexylamine, methyldicyclohexylamine,methyldiheptylamine, methyldioctylamine, methyldinonylamine,methyldidecylamine, ethyldibutylamine, ethyldipentylamine,ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine,ethyldinonylamine, ethyldidecylamine, dicyclohexylmethylamine,tris[2-(2-methoxyethoxy)ethyl]amine, triisopropanolamine,ethylenediamine, tetramethylenediamine, hexamethylenediamine,4,4′-diamino-1,2-diphenylethane,4,4′-diamino-3,3′-dimethyldiphenylmethane,4,4′-diamino-3,3′-diethyldiphenylmethane, 2,2′-methylenebisaniline,imidazole, 4-methylimidazole, pyridine, 4-methylpyridine,1,2-di(2-pyridyl)ethane, 1,2-di(4-pyridyl)ethane,1,2-di(2-pyridyl)ethene, 1,2-di(4-pyridyl)ethene,1,3-di(4-pyridyl)propane, 1,2-di(4-pyridyloxy)ethane,di(2-pyridyl)ketone, 4,4′-dipyridyl sulfide, 4,4′-dipyridyl disulfide,2,2′-dipyridylamine, 2,2′-dipicolylamine, bipyridine and the like,preferably aromatic amines such as diisopropylaniline, and morepreferably 2,6-diisopropylaniline.

Examples of the ammonium salt include tetramethylammonium hydroxide,tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide,tetrahexylammonium hydroxide, tetraoctylammonium hydroxide,phenyltrimethylammonium hydroxide,3-(trifluoromethyl)phenyltrimethylammonium hydroxide,tetra-n-butylammonium salicylate and choline.

The acidity in a salt generating an acid having an acidity lower thanthat of an acid generated from the acid generator (B) is indicated bythe acid dissociation constant (pKa). Regarding the salt generating anacid having an acidity lower than that of an acid generated from theacid generator (B), the acid dissociation constant of an acid generatedfrom the salt usually meets the following inequality: −3<pKa, preferably−1<pKa<7, and more preferably 0<pKa<5.

Examples of the salt generating an acid having an acidity lower thanthat of an acid generated from the acid generator (B) include saltsrepresented by the following formulas, a salt represented by formula (D)mentioned in JP 2015-147926 A (hereinafter sometimes referred to as“weak acid inner salt (D)”, and salts mentioned in JP 2012-229206 A, JP2012-6908 A, JP 2012-72109 A, JP 2011-39502 A and JP 2011-191745 A. Thesalt generating an acid having an acidity lower than that of an acidgenerated from the acid generator (B) is preferably a weak acid innersalt (D).

Examples of the weak acid inner salt (D) include the following salts.

When the resist composition includes the quencher (C), the content ofthe quencher (C) in the solid component of the resist composition isusually 0.01 to 5% by mass, and preferably 0.01 to 3% by mass.

<Other Components>

The resist composition of the present invention may also includecomponents other than the components mentioned above (hereinaftersometimes referred to as “other components (F)”). The other components(F) are not particularly limited and it is possible to use variousadditives known in the resist field, for example, sensitizers,dissolution inhibitors, surfactants, stabilizers and dyes.

<Preparation of Resist Composition>

The resist composition of the present invention can be prepared bymixing a salt (I) and a resin (A), and if necessary, an acid generator(B), resins other than the resin (A), a solvent (E), a quencher (C) andother components (F). The order of mixing these components is any orderand is not particularly limited. It is possible to select, as thetemperature during mixing, appropriate temperature from 10 to 40° C.,according to the type of the resin, the solubility in the solvent (E) ofthe resin and the like. It is possible to select, as the mixing time,appropriate time from 0.5 to 24 hours according to the mixingtemperature. The mixing means is not particularly limited and it ispossible to use mixing with stirring.

After mixing the respective components, the mixture is preferablyfiltered through a filter having a pore diameter of about 0.003 to 0.2μm.

<Method for Producing Resist Pattern>

The method for producing a resist pattern of the present inventioninclude:

(1) a step of applying the resist composition of the present inventionon a substrate,(2) a step of drying the applied composition to form a compositionlayer,(3) a step of exposing the composition layer,(4) a step of heating the exposed composition layer, and(5) a step of developing the heated composition layer.

The resist composition can be usually applied on a substrate using aconventionally used apparatus, such as a spin coater. Examples of thesubstrate include inorganic substrates such as a silicon wafer. Beforeapplying the resist composition, the substrate may be washed, and anorganic antireflection film may be formed on the substrate.

The solvent is removed by drying the applied composition to form acomposition layer. Drying is performed by evaporating the solvent usinga heating device such as a hot plate (so-called “prebake”), or adecompression device. The heating temperature is preferably 50 to 200°C. and the heating time is preferably 10 to 180 seconds. The pressureduring drying under reduced pressure is preferably about 1 to 1.0×10⁵Pa.

The composition layer thus obtained is usually exposed using an aligner.The aligner may be a liquid immersion aligner. It is possible to use, asan exposure source, various exposure sources, for example, exposuresources capable of emitting laser beam in an ultraviolet region such asKrF excimer laser (wavelength of 248 nm), ArF excimer laser (wavelengthof 193 nm) and F₂ excimer laser (wavelength of 157 nm), an exposuresource capable of emitting harmonic laser beam in a far-ultraviolet orvacuum ultra violet region by wavelength-converting laser beam from asolid-state laser source (YAG or semiconductor laser), an exposuresource capable of emitting electron beam or EUV and the like. In thepresent specification, such exposure to radiation is sometimescollectively referred to as “exposure”. The exposure is usuallyperformed through a mask corresponding to a pattern to be required. Whenelectron beam is used as the exposure source, exposure may be performedby direct writing without using the mask.

The exposed composition layer is subjected to a heat treatment(so-called “post-exposure bake”) to promote the deprotection reaction inan acid-labile group. The heating temperature is usually about 50 to200° C., and preferably about 70 to 150° C.

The heated composition layer is usually developed with a developingsolution using a development apparatus. Examples of the developingmethod include a dipping method, a paddle method, a spraying method, adynamic dispensing method and the like. The developing temperature ispreferably, for example, 5 to 60° C. and the developing time ispreferably, for example, 5 to 300 seconds. It is possible to produce apositive resist pattern or negative resist pattern by selecting the typeof the developing solution as follows.

When the positive resist pattern is produced from the resist compositionof the present invention, an alkaline developing solution is used as thedeveloping solution. The alkaline developing solution may be variousaqueous alkaline solutions used in this field. Examples thereof includeaqueous solutions of tetramethylammonium hydroxide and(2-hydroxyethyl)trimethylammonium hydroxide (commonly known as choline).The surfactant may be contained in the alkaline developing solution.

It is preferable that the developed resist pattern is washed withultrapure water and then water remaining on the substrate and thepattern is removed.

When the negative resist pattern is produced from the resist compositionof the present invention, a developing solution containing an organicsolvent (hereinafter sometimes referred to as “organic developingsolution”) is used as the developing solution.

Examples of the organic solvent contained in the organic developingsolution include ketone solvents such as 2-hexanone and 2-heptanone;glycol ether ester solvents such as propylene glycol monomethyl etheracetate; ester solvents such as butyl acetate; glycol ether solventssuch as propylene glycol monomethyl ether; amide solvents such asN,N-dimethylacetamide; and aromatic hydrocarbon solvents such asanisole.

The content of the organic solvent in the organic developing solution ispreferably 90% by mass or more and 100% by mass or less, more preferably95% by mass or more and 100% by mass or less, and still more preferablythe organic developing solution is substantially composed of the organicsolvent.

Particularly, the organic developing solution is preferably a developingsolution containing butyl acetate and/or 2-heptanone. The total contentof butyl acetate and 2-heptanone in the organic developing solution ispreferably 50% by mass or more and 100% by mass or less, more preferably90% by mass or more and 100% by mass or less, and still more preferablythe organic developing solution is substantially composed of butylacetate and/or 2-heptanone.

The surfactant may be contained in the organic developing solution. Atrace amount of water may be contained in the organic developingsolution.

During development, the development may be stopped by replacing by asolvent with the type different from that of the organic developingsolution.

The developed resist pattern is preferably washed with a rinsingsolution. The rinsing solution is not particularly limited as long as itdoes not dissolve the resist pattern, and it is possible to use asolution containing an ordinary organic solvent which is preferably analcohol solvent or an ester solvent.

After washing, the rinsing solution remaining on the substrate and thepattern is preferably removed.

(Application)

The resist composition of the present invention is suitable as a resistcomposition for exposure of KrF excimer laser, a resist composition forexposure of ArF excimer laser, a resist composition for exposure ofelectron beam (EB) or a resist composition for exposure of EUV,particularly a resist composition for exposure of ArF excimer laser, andthe resist composition is useful for fine processing of semiconductors.

EXAMPLES

The present invention will be described more specifically by way ofExamples. Percentages and parts expressing the contents or amounts usedin the Examples are by mass unless otherwise specified.

The weight-average molecular weight is a value determined by gelpermeation chromatography. Analysis conditions of gel permeationchromatography are as follows.

Column: TSKgel Multipore IIXL-M×3+guardcolumn (manufactured by TOSOHCORPORATION)

Eluent: tetrahydrofuran

Flow rate: 1.0 mL/min

Detector: RI detector

Column temperature: 40° C.

Injection amount: 100 μl

Molecular weight standards: polystyrene standard (manufactured by TOSOHCORPORATION)

Structures of compounds were confirmed by measuring a molecular ion peakusing mass spectrometry (Liquid Chromatography: Model 1100, manufacturedby Agilent Technologies, Inc., Mass Spectrometry: Model LC/MSD,manufactured by Agilent Technologies, Inc.). The value of this molecularion peak in the following Examples is indicated by “MASS”.

Example 1: Synthesis of Salt Represented by Formula (I-16)

10 Parts of a compound represented by formula (I-16-a), 12.76 parts of acompound represented by formula (I-16-b), 11.50 parts of potassiumcarbonate, 2.88 parts of potassium iodide and 50 parts of acetone weremixed, and the mixture was stirred under reflux at 58° C. for 29 hoursand then concentrated. To the concentrate thus obtained, 15 parts ofethyl acetate and 22 parts of an aqueous 10% sodium hydroxide solutionwere added, followed by stirring and further separation. This alkaliwashing was performed twice. To the organic layer thus obtained, 22parts of ion-exchanged water was added, followed by stirring and furtherseparation. This water washing was performed three times. The organiclayer thus obtained was concentrated, followed by separation from theconcentrate thus obtained with a column (Merck, silica gel 60-200 mesh,developing solvent: n-heptane) to obtain 12.17 parts of a compoundrepresented by formula (I-16-c).

To 11.08 parts of methanesulfonic acid, 1.11 parts of diphosphoruspentoxide was added, followed by stirring at 23° C. for 30 minutes. Tothe mixture thus obtained, 4.47 parts of a compound represented byformula (I-16-c) was added. After cooling to 5° C., 3.08 parts of acompound represented by formula (I-16-d) was added dropwise over 5minutes, followed by stirring at 5° C. for 20 minutes, stirring at 23°C. for 4 hours and further stirring at 50° C. for 12 hours. The mixturethus obtained was cooled to 5° C. and 55 parts of ion-exchanged waterwas added, followed by neutralization due to the addition of 15 parts ofan aqueous 28% ammonia solution to obtain a solution containing a saltrepresented by formula (I-16-e). To the solution containing a saltrepresented by formula (I-16-e), a mixed solution of 6.40 parts of asalt represented by formula (I-16-f) and 51.23 parts of chloroform wasadded, followed by stirring at 23° C. for 24 hours and furtherseparation. To the organic layer thus obtained, 25 parts ofion-exchanged water was added, followed by stirring and furtherseparation. This water washing was performed five times. To the organiclayer thus obtained, 1.00 parts of activated carbon was added, followedby stirring at 23° C. for 30 minutes and further filtration. Thefiltrate thus obtained was concentrated and 30 parts of n-heptane wasadded to the residue thus obtained, followed by stirring, removal of thesupernatant and further concentration. To the concentrate thus obtained,30 parts of tert-butyl methyl ether was added, followed by stirring,removal of the supernatant and further concentration to obtain 2.31parts of a salt represented by formula (I-16).

MASS (ESI (+) Spectrum): M⁺ 303.1

MASS (ESI (−) Spectrum): M⁻ 279.9

Example 2: Synthesis of Salt Represented by Formula (I-1)

To 13.46 parts of methanesulfonic acid, 1.35 parts of diphosphoruspentoxide was added, followed by stirring at 23° C. for 30 minutes. Tothe mixture thus obtained, 3.00 parts of a compound represented byformula (I-1-c) was added. After cooling to 5° C., 2.62 parts of acompound represented by formula (I-16-d) was added dropwise over 5minutes, followed by stirring at 5° C. for 20 minutes and furtherstirring at 23° C. for 4 hours. The mixture thus obtained was cooled to5° C. and 30 parts of ion-exchanged water was added, followed byneutralization due to the addition of 15 parts of an aqueous 28% ammoniasolution to obtain a solution containing a salt represented by formula(I-1-e). To the solution containing a salt represented by formula(I-1-e), a mixed solution of 5.44 parts of a salt represented by formula(I-16-f) and 43.55 parts of chloroform was added, followed by stirringat 23° C. for 18 hours and further separation. To the organic layer thusobtained, 20 parts of ion-exchanged water was added, followed bystirring and further separation. This water washing was performed fivetimes. The organic layer thus obtained was concentrated and 30 parts oftert-butyl methyl ether was added to the residue thus obtained, followedby stirring and filtration to obtain 6.43 parts of a salt represented byformula (I-1).

MASS (ESI (+) Spectrum): M⁺ 261.1

MASS (ESI (−) Spectrum): M⁻ 279.9

Example 3: Synthesis of Salt Represented by Formula (I-61)

To 13.46 parts of methanesulfonic acid, 1.35 parts of diphosphoruspentoxide was added, followed by stirring at 23° C. for 30 minutes. Tothe mixture thus obtained, 3.00 parts of a compound represented byformula (I-1-c) was added. After cooling to 5° C., 2.58 parts of acompound represented by formula (I-61-d) was added dropwise over 5minutes, followed by stirring at 5° C. for 20 minutes and furtherstirring at 23° C. for 4 hours. The mixture thus obtained was cooled to5° C. and 30 parts of ion-exchanged water was added, followed byneutralization due to the addition of 15 parts of an aqueous 28% ammoniasolution to obtain a solution containing a salt represented by formula(I-61-e). To the solution containing a salt represented by formula(I-61-e), a mixed solution of 5.44 parts of a salt represented byformula (I-16-f) and 43.55 parts of chloroform was added, followed bystirring at 23° C. for 18 hours and further separation. To the organiclayer thus obtained, 20 parts of ion-exchanged water was added, followedby stirring and further separation. This water washing was performedfive times. The organic layer thus obtained was concentrated and 30parts of tert-butyl methyl ether was added to the residue thus obtained,followed by stirring and further filtration to obtain 6.36 parts of asalt represented by formula (I-61).

MASS (ESI (+) Spectrum): M⁺ 259.1

MASS (ESI (−) Spectrum): M⁻ 279.9

Example 4: Synthesis of Salt Represented by Formula (I-41)

10 Parts of a compound represented by formula (I-16-a), 13.87 parts of acompound represented by formula (I-41-b), 11.50 parts of potassiumcarbonate, 2.88 parts of potassium iodide and 50 parts of acetone weremixed, and the mixture was stirred under reflux at 58° C. for 29 hoursand then concentrated. To the concentrate thus obtained, 15 parts ofethyl acetate and 22 parts of an aqueous 10% sodium hydroxide solutionwere added, followed by stirring and further separation. This alkaliwashing was performed twice. To the organic layer thus obtained, 22parts of ion-exchanged water was added, followed by stirring and furtherseparation. This water washing was performed three times. The organiclayer thus obtained was concentrated, followed by separation from theconcentrate thus obtained with a column (Merck, silica gel 60-200 mesh,developing solvent: n-heptane) to obtain 12.44 parts of a compoundrepresented by formula (I-41-c).

To 11.08 parts of methanesulfonic acid, 1.11 parts of diphosphoruspentoxide was added, followed by stirring at 23° C. for 30 minutes. Tothe mixture thus obtained, 4.83 parts of a compound represented byformula (I-41-c) was added. After cooling to 5° C., 3.08 parts of acompound represented by formula (I-16-d) was added dropwise over 5minutes, followed by stirring at 5° C. for 20 minutes, stirring at 23°C. for 4 hours and further stirring at 50° C. for 12 hours. The mixturethus obtained was cooled to 5° C. and 55 parts of ion-exchanged waterwas added, followed by neutralization due to the addition of 15 parts ofan aqueous 28% ammonia solution to obtain a solution containing a saltrepresented by formula (I-41-e). To the solution containing a saltrepresented by formula (I-41-e), a mixed solution of 6.40 parts of asalt represented by formula (I-16-f) and 51.23 parts of chloroform wasadded, followed by stirring at 23° C. for 24 hours and furtherseparation. To the organic layer thus obtained, 25 parts ofion-exchanged water was added, followed by stirring and furtherseparation. This water washing was performed five times. To the organiclayer thus obtained, 1.00 parts of activated carbon was added, followedby stirring at 23° C. for 30 minutes and further filtration. Thefiltrate thus obtained was concentrated and 30 parts of n-heptane wasadded to the residue thus obtained, followed by stirring, removal of thesupernatant and further concentration. To the concentrate thus obtained,30 parts of tert-butyl methyl ether was added, followed by stirring,removal of the supernatant and further concentration to obtain 2.44parts of a salt represented by formula (I-41).

MASS (ESI (+) Spectrum): M⁺ 319.1

MASS (ESI (−) Spectrum): M⁻ 279.9

Example 5: Synthesis of Salt Represented by Formula (I-20)

To 11.08 parts of methanesulfonic acid, 1.11 parts of diphosphoruspentoxide was added, followed by stirring at 23° C. for 30 minutes. Tothe mixture thus obtained, 4.47 parts of a compound represented byformula (I-16-c) was added. After cooling to 5° C., 3.08 parts of acompound represented by formula (I-16-d) was added dropwise over 5minutes, followed by stirring at 5° C. for 20 minutes, stirring at 23°C. for 4 hours and further stirring at 50° C. for 12 hours. The mixturethus obtained was cooled to 5° C. and 55 parts of ion-exchanged waterwas added, followed by neutralization due to the addition of 15 parts ofan aqueous 28% ammonia solution to obtain a solution containing a saltrepresented by formula (I-16-e). To the solution containing a saltrepresented by formula (I-16-e), a mixed solution of 6.67 parts of asalt represented by formula (I-20-f) and 51.23 parts of chloroform wereadded, followed by stirring at 23° C. for 24 hours and furtherseparation. To the organic layer thus obtained, 25 parts ofion-exchanged water was added, followed by stirring and furtherseparation. This water washing was performed five times. To the organiclayer thus obtained, 1.00 parts of activated carbon was added, followedby stirring at 23° C. for 30 minutes and further filtration. Thefiltrate thus obtained was concentrated and 30 parts of n-heptane of theresidue thus obtained was added, followed by stirring, removal of thesupernatant and further concentration. To the concentrate thus obtained,30 parts of tert-butyl methyl ether was added, followed by stirring,removal of the supernatant and further concentration to obtain 2.29parts of a salt represented by formula (I-20).

MASS (ESI (+) Spectrum): M⁺ 303.1

MASS (ESI (−) Spectrum): M⁻ 291.9

Example 6: Synthesis of Salt Represented by Formula (I-65)

To 13.46 parts of methanesulfonic acid, 1.35 parts of diphosphoruspentoxide was added, followed by stirring at 23° C. for 30 minutes. Tothe mixture thus obtained, 3.00 parts of a compound represented byformula (I-1-c) was added. After cooling to 5° C., 2.58 parts of acompound represented by formula (I-61-d) was added dropwise over 5minutes, followed by stirring at 5° C. for 20 minutes and furtherstirring at 23° C. for 4 hours. The mixture thus obtained was cooled to5° C. and 30 parts of ion-exchanged water was added, followed byneutralization due to the addition of 15 parts of an aqueous 28% ammoniasolution to obtain a solution containing a salt represented by formula(I-61-e). To the solution containing a salt represented by formula(I-61-e), a mixed solution of 5.67 parts of a salt represented byformula (I-20-f) and 43.55 parts of chloroform was added, followed bystirring at 23° C. for 18 hours and further separation. To the organiclayer thus obtained, 20 parts of ion-exchanged water was added, followedby stirring and further separation. This water washing was performedfive times. The organic layer thus obtained was concentrated and 30parts of tert-butyl methyl ether was added to the residue thus obtained,followed by stirring and further filtration to obtain 6.11 parts of asalt represented by formula (I-65).

MASS (ESI (+) Spectrum): M⁺ 259.1

MASS (ESI (−) Spectrum): M⁻ 291.9

Synthesis of Resin (A)

Compounds (monomers) used in the synthesis of the resin (A) are shownbelow. Hereinafter, these compounds are referred to as “monomer(a1-1-2)” according to the number of formula.

Synthesis Example 1 [Synthesis of Resin A1]

A monomer (a1-1-2), a monomer (a1-2-5), a monomer (a2-1-1) and a monomer(a3-1-1) were mixed in a molar ratio of 5:42:32:21 [monomer(a1-1-2):monomer (a1-2-5):monomer (a2-1-1):monomer (a3-1-1)], andpropylene glycol monomethyl ether acetate was added in the amount of 2mass times the total amount of all monomers to obtain a solution. Tothis solution, azobisisobutyronitrile andazobis(2,4-dimethylvaleronitrile) as initiators were added in theamounts of 1 mol % and 3 mol % based on the total amount of allmonomers, followed by heating at 75° C. for about 5 hours. The reactionmixture thus obtained was poured into a large amount of a methanol/watermixed solvent to precipitate a resin, and this resin was filtered. Afterperforming a reprecipitation operation in which a solution, which isobtained by dissolving the resin thus obtained in propylene glycolmonomethyl ether acetate, is again poured into a methanol/water mixedsolvent to precipitate a resin, and this resin is filtered, twice, aresin A1 having a weight-average molecular weight of 9.1×10³ wasobtained in a yield of 97%. This resin A1 includes the followingstructural units.

Synthesis Example 2 [Synthesis of Resin X1]

Using a monomer (a4-1-4) as a monomer, methyl isobutyl ketone was addedin the amount of 1.2 mass times the total amount of all monomers toobtain a solution. To this solution, azobisisobutyronitrile andazobis(2,4-dimethylvaleronitrile) as initiators were added in theamounts of 0.7 mol % and 2.1 mol % based on the total amount of allmonomers, followed by heating at 75° C. for about 5 hours. The reactionmixture thus obtained was poured into a large amount of a methanol/watermixed solvent to precipitate a resin, and this resin was filtered. Theresin thus obtained was repulped in a methanol/water mixed solvent andthen filtered to obtain a resin X1 having a weight-average molecularweight of 1.7×10⁴ in a yield of 76%. This resin X1 includes thefollowing structural unit.

<Preparation of Resist Compositions>

As shown in Table 7, the following respective components were mixed, andthe mixtures thus obtained were filtered through a fluorine resin filterhaving a pore diameter of 0.2 μm to prepare resist compositions.

TABLE 7 Resist Acid composition Resin generator Salt (I) Quencher (C)PB/PEB Composition 1 X1/A1 = — I-1 = D1 = 90° C./85° C. 0.2/10 parts 1.4parts 0.28 part Composition 2 X1/A1 = — I-16 = D1 = 90° C./85° C. 0.2/10parts 1.4 parts 0.28 part Composition 3 X1/A1 = — I-61 = D1 = 90° C./85°C. 0.2/10 parts 1.4 parts 0.28 part Composition 4 X1/A1 = — I-41 = D1 =90° C./85° C. 0.2/10 parts 1.4 parts 0.28 part Composition 5 X1/A1 = —I-20 = D1 = 90° C./85° C. 0.2/10 parts 1.4 parts 0.28 part Composition 6X1/A1 = — I-65 = D1 = 90° C./85° C. 0.2/10 parts 1.4 parts 0.28 partComparative X1/A1 = IX-1 = — D1 = 90° C./85° C. Composition 1 0.2/10parts 1.4 parts 0.28 part Comparative X1/A1 = IX-2 = — D1 = 90° C./85°C. Composition 2 0.2/10 parts 1.4 parts 0.28 part Comparative X1/A1 =IX-3 = — D1 = 90° C./85° C. Composition 3 0.2/10 parts 1.4 parts 0.28part Comparative X1/A1 = IX-4 = — D1 = 90° C./85° C. Composition 40.2/10 parts 1.4 parts 0.28 part Comparative X1/A1 = IX-5 = — D1 = 90°C./85° C. Composition 5 0.2/10 parts 1.4 parts 0.28 part

<Resin>

A1, X1: Resin A1, Resin X1

<Salt (I)>

I-1: Salt represented by formula (I-1)

I-16: Salt represented by formula (I-16)

I-20: Salt represented by formula (I-20)

I-41: Salt represented by formula (I-41)

I-61: Salt represented by formula (I-61)

I-65: Salt represented by formula (I-65)

<Acid Generator>

IX-1: Salt represented by formula (IX-1) (synthesized in accordance withExamples of JP 2012-106980 A)

IX-2: Salt represented by formula (IX-2) (synthesized in accordance withExamples of JP 2015-143208 A)

IX-3: Salt represented by formula (IX-3) (synthesized in accordance withExamples of JP 2002-268223 A)

IX-4: Salt represented by formula (IX-4) (synthesized in accordance withExamples of JP 2012-168279 A)

IX-5: Salt represented by formula (IX-5) (synthesized in accordance withExamples of JP 2014-224095 A)

<Quencher (C)>

D1: (manufactured by Tokyo Chemical Industry Co., Ltd.)

<Solvent>

Propylene glycol monomethyl ether acetate 265 parts  Propylene glycolmonomethyl ether 20 parts 2-Heptanone 20 parts γ-Butyrolactone 3.5parts 

<Production of Resist Pattern>

A 12-inch silicon wafer with a SiO₂ layer having a thickness of 100 nmformed on a surface was treated with hexamethylsilazane at 120° C. for60 seconds, and then a resist composition was applied thereon by spincoating in such a manner that the thickness of the film after pre-bakingbecame 240 nm.

The silicon wafer coated with the resist composition was pre-baked for60 second on a direct hot plate at the temperature mentioned in the “PB”column in Table 7 to form a composition layer. The composition layerthus formed on the silicon wafer was exposed through a mask for forminga line-and-space pattern (pitch 300 nm/space 114 nm) stepwise withchanging exposure dose, by an ArF excimer laser stepper for immersionlithography (XT:1900Gi by ASML Ltd.: NA=0.90, Annular a out/a in=0.75/0.40, XY-polarization). Ultrapure water was used for medium ofimmersion.

After exposure, post-exposure baking was performed on a hot plate for 60seconds at the temperature mentioned in the “PEB” column in Table 7.Then, paddle development was performed with an aqueous 2.38% by masstetramethylammonium hydroxide solution for 60 seconds to obtain a resistpattern.

Effective sensitivity was represented as the exposure dose at which aresist pattern with a space width of 130 nm was obtained.

(Evaluation of Line Edge Roughness (LER))

A maximum width of irregularities in each wall surface of the obtainedresist pattern was observed using a scanning electron microscope. Thismaximum width was shown in Table 8 as LER (nm).

TABLE 8 Resist composition LER (nm) Example 7 Composition 1 4.02 Example8 Composition 2 4.11 Example 9 Composition 3 4.07 Example 10 Composition4 3.96 Example 11 Composition 5 3.99 Example 12 Composition 6 4.02Comparative Example 1 Comparative Composition 1 4.26 Comparative Example2 Comparative Composition 2 4.23 Comparative Example 3 ComparativeComposition 3 4.52 Comparative Example 4 Comparative Composition 4 4.35Comparative Example 5 Comparative Composition 5 4.21

As is apparent from the above results, a resist pattern with excellentline edge roughness can be produced according to a salt and a resistcomposition comprising an acid generator including the same of thepresent invention.

INDUSTRIAL APPLICABILITY

Since a resist pattern with satisfactory line edge roughness (LER) canbe produced according to a salt and a resist composition comprising anacid generator including the same of the present invention, the resistcomposition is useful for fine processing of semiconductors and isindustrially very useful.

1. A salt represented by formula (I):

wherein, in formula (I), R¹ represents —(X¹—O)_(o)—R⁵, and o representsan integer of 0 to 6, R⁵ represents a hydrocarbon group having 1 to 12carbon atoms, X¹ represents a divalent hydrocarbon group having 2 to 12carbon atoms, R² represents an alkyl group having 1 to 12 carbon atoms,and —CH₂— included in the alkyl group may be replaced by —O— or —CO—, lrepresents an integer of 0 to 3, and when 1 is 2 or more, a plurality ofR² may be the same or different from each other, R³ and R⁴ eachindependently represent a hydrogen atom, a hydroxy group or ahydrocarbon group having 1 to 12 carbon atoms, and —CH₂— included in thehydrocarbon group may be replaced by —O— or —CO—, m and n eachindependently represent 1 or 2, when m is 2, two R³ are the same ordifferent from each other, and when n is 2, two R⁴ are the same ordifferent from each other, X⁰ represents a single bond, —CH₂—, —O— or—S—, and R⁶ and R⁷ each independently represent an alkyl group having 1to 4 carbon atoms which has a fluorine atom, or may be bonded to eachother to form a divalent hydrocarbon group having 2 to 8 carbon atomswhich has a fluorine atom.
 2. The salt according to claim 1, wherein R³and R⁴ are a hydrogen atom, and n and m are
 2. 3. The salt according toclaim 1, wherein o is 0, 1 or
 2. 4. The salt according to claim 1,wherein R⁶ and R⁷ each independently represent a trifluoromethyl group,a perfluoroethyl group or may be bonded to each other to form a divalenthydrocarbon group having 2 to 3 carbon atoms which has a fluorine atom.5. An acid generator comprising the salt according to claim
 1. 6. Aresist composition comprising the acid generator according to claim 5and a resin having an acid-labile group.
 7. The resist compositionaccording to claim 6, wherein the resin having an acid-labile groupincludes at least two of a structural unit represented by formula (a1-1)and a structural unit represented by formula (a1-2):

wherein, in formula (a1-1) and formula (a1-2), L^(a1) and L^(a2) eachindependently represent —O— or *—O—(CH₂)_(k1)—CO—O—, k1 represents aninteger of 1 to 7, and * represents a bonding site to —CO—, R^(a4) andR^(a5) each independently represent a hydrogen atom or a methyl group,R^(a6) and R^(a7) each independently represent an alkyl group having 1to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbonatoms, or a group obtained by combining these groups, m1 represents aninteger of 0 to 14, n1 represents an integer of 0 to 10, and n1′represents an integer of 0 to
 3. 8. The resist composition according toclaim 6, further comprising a salt generating an acid having an aciditylower than that of an acid generated from the acid generator.
 9. Theresist composition according to claim 6, further comprising a resinincluding a structural unit having a fluorine atom.
 10. A method forproducing a resist pattern, which comprises: (1) a step of applying theresist composition according to claim 6 on a substrate, (2) a step ofdrying the applied composition to form a composition layer, (3) a stepof exposing the composition layer, (4) a step of heating the exposedcomposition layer, and (5) a step of developing the heated compositionlayer.